Another type for thermal battery: ice thermal storage. Instead of running AC, it’s a freezer that makes ice during the night (using off-peak electricity and taking advantage of the cooler nighttime air) and then melts it during the day to cool large buildings. They’re a ridiculously good idea if you’re running a large enough HVAC system - they can even lower capital costs compared to traditional systems. Unfortunately, many building operators don’t use them because they’re unfamiliar with the technology or because they take up more building footprint. https://en.m.wikipedia.org/wiki/Ice_storage_air_conditioning
From their website I gleaned that they have 5 facilities, and several miles of piping that carries ice-cold water to their customers, large buildings around.
It's the maximally outsourced air-conditioning solution I ever saw :)
There’s versions of this in NYC that use the bay as a first pass heat exchanger. Not sure how deep or cold the Chicago river is but I’d think they’d be able to do the same.
FWIW they suck at their job.
Every year there are some days where we don't have AC in the office during summer because they stop sending cold water to the building I work in.
Probably not, because there's a second interesting fact about the system (which I just learned): the water isn't returned to the lake directly.
Instead it's used as an input to the filtration plants, cleaned, and used as municipal water. I'm not sure what the overall effect of getting slightly warmer water in the municipal system is, but I bet it's a win overall since we spend so much energy heating up water (as per the article!).
Edit: also the lake is 1600 cubic km of water, so I dunno if we could ever noticeably change the lake temperature this way.
1600 km³ × .1 kcal/ℓ is 670 petajoules, so that's the energy input you'd need to heat the lake up by 0.1°. World marketed energy consumption is about 20 TW, so the entire world economy could heat the lake up at about 0.23° per day if you covered it in a blanket first. So it's not completely out of the question, but only 2.7 million people live in Toronto, so Toronto probably only uses about 20 GW.
By comparison, the lake's surface area is 19000 km², so when the sun is shining on it (at a slanting angle, as it always does that far north), it's receiving about 10 TW of solar energy, half the amount used by the entire human economy. It reflects about 10% of that into space and converts the rest into heat, then re-emits it as longwave infrared light, half at night.
There's a local university that uses this method to cool their musical performance space, which causes it to be comfortably cold but without the noise of AC.
Surprisingly simple design, actually. The water sits in a large tank with plenty of room to expand and contract. Pipes filled with refrigerant run inside the tank. Here’s a photo: https://images.app.goo.gl/Td6RdFbuVE8QJAmu6
This seems like it could backfire if we start to get the majority of our electricity from solar, though, right? Nighttime may not always be considered off-peak.
Well you’d just make the ice whenever it’s cheapest, taking into account the effects of cold air and of electricity prices. In the future it might make sense to make the ice when it’s warm out because power is nearly free at those times. But a smart building automation system could know when cloud cover is predicted and make ice the night before.
One company tried to make a residential version (called Ice Bear, IIRC), but it was unsuccessful. There’s no reason it couldn’t be practical, though. Especially with something like some prototype concepts which propose putting all heating and cooling appliances (refrigerator, water heater, HVAC, and possibly even a drying machine) on a single heat pump loop, ice thermal storage could become economical for single family homes in the near future.
Am I the only one that find this article incredibly confusing?
It starts off talking about wanting to move energy production to renewable sources. Great, I'm with you so far. A major issue with renewable energy (solar and wind) is that they're variable, not constant. This results in uneven power. The wind doesn't blow, it's cloudy or it's night time. So we need a way to convert this variable renewable energy into constant energy that's accessible around the clock. An obvious solution to the problem is to convert the renewable energy into stored potential energy. This is what pumped hydroelectric dams are all about. Use the variable energy to pump a bunch of water up behind a dam, then release it when you need a more constant supply of energy.
Great, so we've got that much figured out. The world needs a way to convert renewable energy into constant energy.
And the solution to this problem is... the distribution of more efficient water heaters.
Wat
How do more efficient water heaters in any way, shape or form help solve the renewable variable rate energy to constant energy problem? I feel like I must be missing something obvious. Are we able to somehow store energy in heat-pump based water heaters and then extract that energy to run other items in our homes? When you store energy in a heat-pump based water heater does it not need to run at night when renewable energy sources are lowest?
Can anyone explain to me what the heck this article is talking about?
I feel like I'm missing the larger picture, but I don't see how these two concepts (energy storage and appliance efficiency) are related.
> How do more efficient water heaters in any way, shape or form help solve the renewable variable rate energy to constant energy problem? I feel like I must be missing something obvious
A large portion of our world energy use is to make heat. Thus if you can make the heat you need when there is plenty of renewable energy available, and then store it for use latter that is a large win. Sure we can't turn that heat back into electricity (false, but they are not worth talking about), but since heat is the goal that doesn't matter.
This is well understood. My parents have been on a off-peak water heating program since 1988 (in all those years they only ran out of hot water 5 times, and nobody was trying to save water). Based on that experience, just the hot water a family uses in a day is in the 300-800 liters range (go high - running out of hot water for the day sucks). Heating your house is a lot more though - 40000 liters is a low end estimate I've seen.
You won't be cooking food, powering your car, or lighting your house this way, but it is still a cheap and useful way to store energy. It is also something we can do for the world using yesterday's cheap technology.
Good points! I'm certainly in favor of time-shifting demand to meet supply to maximally utilize renewables. Let's grab as much of this low hanging as we can.
I just thought the framework of his argument was rather odd. Better water heaters are framed as being a way to avoid constructing power storage systems that convert variable renewable energy into steady baseline power, which feels like an argument that doesn't hold up. We'll still need some way to supply steady power to run AC units, heaters, and other big power draws all night, no matter what type of water heaters we use!
The idea was that you run the water heaters at a time when demand for electricity is low, and supply is high. The water will stay warm for quite some time and can be used later. For example - run the water heater at 3am during a windy night, so people can shower in the morning
The point is, that we can move demand around. The smart water-heaters with the ability to store heat are not only more efficient, they can be run when a lot of electricity is available and can be shut off, when there isn't. Yes, we also will need some amount of storage to produce electricity when demand exceeds production, moving the time of demand goes a long way on managing renewables.
The big point is demand response in smart heaters allowing time shifting.
He also, confusingly, makes a second point about how efficiency can to avoid building powerplants/storage.
Replacing old inefficient heaters with new smart and efficient heaters is a double win.
If you power them from renewables it's a triple win.
Also night time energy is often low carbon because of nuclear and wind combined with low demand, but modern smart heaters can respond at a much smaller scale to use "excess" energy.
> The world needs a way to convert renewable energy into constant energy.
Not really or at least that represents a gross simplification of the situation.
Electricity demand is anything but constant - peak to trough intraday consumption can vary by up to a factor of 5. Grid engineering is all about matching lots of different sources with different generation characteristics with a varying (but quite predictable) demand curve.
All generation sources are intermittent - they are just intermittent in different ways. Solar and wind have well known limitations in this regard but at least the variation in output is predictable - particular solar, wind is typically accurately predictable up to a few weeks horizon.
The intermittency associated with thermal plants may be less in some ways but it has the disadvantage is that it is largely not predictable. For example, the average US coal plant will be unavailable for generation 15% of the time - so roughly 1 hour down for every 6 hours generating. Most of this 1 hour downtime is unscheduled/forced which is unpredictable. It's a myth that having a 1GW of fossil fuel generation capacity means you can reliability meet a peak demand of 1GW.
Also nuclear and coal are NOT good at load following - they operate most efficiently when producing the constant design output. Ramping up/down coal or nuclear output quickly is often not at all possible or is possible - depending on plant design - but with a large loss in efficiency and increased plant stresses and wear and tear.
Grid engineers have been maintaining this balancing act between unreliable generation and fluctuating demand for ever. In the past the focus was on coping with the intermittency caused by the failure modes of thermal plants. Increasingly now they are coping with the variable output of solar and wind generation but seem to be managing this - a bunch of European countries source more than 40% of their electricity from solar or wind and none required utility scale li-ion or have experienced increased grid instability.
The same tools are used to handle wind and solar intermittency as are used to handle thermal plant failure or inability to ramp up/down quickly - some hydro storage, backup idling natural gas plants, grid interconnections, etc.
Fundamentally the renewables revolution is happening quietly in the background is driven by simple economics. Coal and nuclear are just too expensive by a factor of 2 or 3 and natural gas, on-shore wind and utility scale solar are just so cheap in comparison. It's cheaper now to build a load of wind (or solar) and some backup natural gas generation - typically with a capacity factor of only 10% or so - than it is to meet demand with thermal fossil fuels. This is because wind and solar are capital intensive while NG plants are cheap to build but expensive to operate due to fuel costs. This combo (idling natural gas and wind and/or solar) is in the process of displacing everything else. 90% of the new generation capacity added in the US last year was of this nature. And a similar proportion is observed globally.
Meanwhile you have endless arguments about why wind and solar "cannot work" in fora, while all around the world it clearly IS working and analysis suggests it requires no technology breakthrough to get to 60%-70% carbon-free generation - many grids are well along this journey (40% to 50%) and none of the doomsday scenarios of massive load shedding, black-outs, etc. have occurred.
My utility solar cost average 50% over regular electricity $ for 2 years.
Texas suffered a doomsday scenario last winter, power demand far exceeding renewables ability under prolonged bad weather. California has frequent rolling blackouts; bizarrely, solar roofs are disallowed to supply the homes they cover.
Where in the world do you live out of interest? There must be some unusual local conditions that would cause that price discrepancy because I've followed the electricity prices in a number of European countries as they've increased their reliance on wind turbines and have seen no obvious kinks in the plots of prices as wind has contributed more and more. Certainly wholesale electricity prices - where I've followed them - are at a historic low at the moment but there is a lot on the demand side that could be causing this.
The Texas story actually reinforces one of my points - thermal fossil fuel plants are unreliable also as the failure of thermal plants caused a far greater loss in capacity than that lost by renewables.
California's electricity has been a mess for decades before the recent growth in solar and wind so I'm not sure how you can claim a causal relationship between what's happening now in California and the expansion of wind and solar.
Regarding domestic roof-top solar PV - I currently don't see it having any role to play in the march towards carbon-free energy - the cost per KWh is just too high and in many countries is only made viable by large government grants and feed-in tariff guarantees which effectively allow a domestic installation to exploit the grid like a giant infinite and free battery. Utility scale solar is completely different - it costs about 1/5 of the price per KWh compared to roof-top domestic PV and in many markets is now competing and beating conventional thermal generation on price without government support.
The main cause of Texas's blackouts were the grid losing about 70% of their natural gas power (and not having good inter-connects with the rest of the US). Also, it is a great example of where the ability to pre-heat a ton of water would have been really useful. If they had the ability to do so, it would have greatly reduced the demands on the grid when the storm hit, which would have prevented the problem in the first place.
Maybe this author has a stake in some up-and-coming smart water heater company whose sales pitch is that they only heat up the tanks when it would use only renewable energy?
In Northern Europe heat pumps are now pretty much standard for new homes. They reduce heating bills quite dramatically compared to other technology. In particular if combined with solar power.
One big advantage is that they can also be run in reverse so you could cool the house in summer (although you might need a special heat pump to do this, especially to separate from the hot water). In areas where it gets very cool, one can also use connect the heat pump to the ground as heat sink which improves efficiency even more.
Another thing Northern Europe has going for it is that we generally go all-in on insulation. 300mm of insulation are norm in newly built house, meaning you can heat a whole house above the Arctic line with less than 5000 kWh a year.
Insulation is _dirt cheap_ compared to lifetime heating costs AND it also keeps the house cool during the summer. Such a no-brainer.
Out of curiosity, what is the effect of this thick insulation on indoor CO₂ levels? Do these houses usually have ventilation systems that can compensate?
Yes you need active ventilation systems, because the thermal efficiency is highly dependant on the house being airtight - to the point where efficiency scores are calculated by overpressuring the house (basically taping a huge fan into the front door with all other doors and windows shut) and measuring the pressure loss. When applying insulation, contractors have to meticulously use foam to seal everything up. It's a major part of the work when building a new house and just a few mistakes can seriously affect thermal performance.
Our house (with a ground based heat pump) uses active ventilation with heat exchangers (and pollen filters) and as a result we have better indoor air than we've had in rented flats in all years before.
Usually heat exchanger ventilations. Fresh air comes in and exchanges heat with used air coming out, so you get fresh air but with the indoor temperature.
HRV (Heat Recovery Ventilator) systems are really cool, too. They solve the ages old problem of bringing fresh air into a home without losing all of the temperature and humidity from the internal environment.
They are designed for a number of air changes per hour/day which would be analogous I guess. I can't remember the number but a Google will tell you, it's different depending on the kind of environment (office/home etc)
We have insulation thickness standards in the US, varying by weather "zone", but for residential construction they seem to be lightly enforced, and efficiency tests are rare to non-existant. (For an illustration of how we typically insulate, see [0].)
It's only one data point, but I'm in New England and from my home office I've watched builders replace 3 1960's-era homes with large colonials. Each is insulated with fiberglass, no visible foam, and nothing outside the sheathing (exterior plywood) except vapor paper / tyvek.
Sure, it meets code requirements for inches of insulation, but it's far from air tight or efficient.
The isolation is made to keep the house hot. About 10 degrees hotter then the outside (without the heater on). This is usually not a problem as temperatures are around 15 during the summer and you can open a few windows to let the hot air out. It does become a problem however when we get extreme temperatures like +30 C as you cant lower the temp by opening a window. Compared to south europe and other warm climates where the houses are built to stay cool.
It basically becomes a greenhouse if you have windows, and of course the windows have three layers which prevents the precious warm air to leak out. Also the roof is black metal. You basically don't need to have the heater on if it's a sunny winter day - because the heating from the sun.
The biggest problem though is the dryness during the winter, cold air comes in and expands, lowering the relative humidity, warm moisturous air is pushed out by mechanical fans. You get extreme dryness, lower then in the desert, which is not good for mucus membranes. I believe that if we could revolutionise air conditioning systems we could prevent the next pandemic (and maybe help the global climate).
If you are only worried about natural cooling, insulation is not the answer. You want a poor insulated house with a lot of shade, and large open windows for the wind to blow through.
Most people these days want more than natural cooling. As soon as you decide to have an AC system installed more insulation is better for the reasons you state.
No. You never want poor insulation. Poor insulation means that the indoor temperature will always match outdoor temperature. There's not such thing as "natural cooling", only thermodynamics.
It depends on the insulation type. If you're using mass as insulation, it can keep the house very cool. This is a common effect in stone houses and barns as they stay closer to the average daily/weekly tempature because it takes a long time for the tempature of that much mass to change.
Mass ≠ insulation. You can have mass as a buffer and regulator, but normally stone or brick and mortar houses simply shift the issues to later in the hot season. It is usually a more even temperature over any given timespan though, as you say.
I'd think barns would have very low mass in comparison to their size, but would stay close to surrounding temp by way of having very little insulation and being very "drafty"
Yes, they aren't the same but can be applied to a similar end goal.
It doesn't completely shift the issue to later in the season. Yes, it will shift some of it, but you still have the night/day average effect. This can still be beneficial, especially if in a shady location.
Barns can be drafty if you are talking about wooden barns. Stone barns, or stone foundation barns built into a hillside, can actually be cooler inside than outside during the heat of the day. That's part of why horse owner sometimes leave their animals in the barn during the day and turn them out at night (typical summer schedule).
Europe has milder winters than many parts of the world. A downside of a heat pump is the limitation on temperature range. A heat pump could never be used in Minnesota, people would freeze.
Ground source heat pumps work anywhere. Also, it's common to have a heat pump paired with resistance heating for when you're pushing the bottom of the range where the heat pump is useful (somewhere between -10 and 20℉ depending on the hardware).
That has similar issues with peak load to AC in the summer but most people do not live in places which are consistently so cold that you don't have a significant amount of time where the heat pump efficiency savings are substantial. As a matter of public policy, encouraging systems which work for 90% of the population is an easy call — especially because that can pair with code changes and subsidies which work anywhere (insulation, install of ground cooling loops, efficiency improvements, etc.).
A ground source heat pump costs at least 3X a normal heat pump. The payback period might not make snese versus a furnace in most cases where extreme cold (below 10F) is common.
The more inhabited parts of Alaska are milder climates than MN, despite being northern they have an ocean to moderate the temperatures. Ground source heat pumps work fine in both MN and the most remote parts of Alaska - but at a much higher cost to install.
Is it possible to hook up computer heat sinks to these things? I figure it'd be better to pump the heat outside my home instead of dissipating it into my air conditioned rooms...
That'd be cool. Those things make a lot of noise. Would be nice if the refrigeration hardware itself was located as far as possible from the living areas.
What if homes had some kind of centralized modular heat exchanging infrastructure? That way we could move heat from hot things that need to be cold to cold things that need to be hot. Move heat from my computers to a water heater or something. Gotta use all that excess heat for something, right?
> One big advantage is that they can also be run in reverse
I don't get why this is an advantage. That's just plain old air conditioning, which is genreally considered to be a wasteful, energy guzzling luxury in colder climates.
Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis.
Heat exchange in the house happens through floor heating. So during a hit summer, the reverse capability just pumps the cold water through our floors (controlled for the dew point) and the warm floor water into the ground. That, combined with controlled ventilation over a physical heat exchanger, keeps the warmth out. Or, during cool seasons, the warmth in.
Our heat pump uses about 1 Kwh electricity (from ecological resources like water or wind only) to generatev3 to 4 Kwh of heating. Without producing carbon dioxide. Airflow based heat pumps are less efficient, and more noisy outside, of course.
> Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis.
Good point. The source and destination of heat can be air, water, or "ground source". But it's still all just the same concept as A/C units. Pump heat to one place, using less energy than what it would take to heat it using resistance heating. There is nothing special about ground source heat pumps, except that they're a pain to install in densely populated areas.
All types of heat pumps, unfortunately, often leak. Depending on the type of refrigerant they use, this can be a serious climate concern as well.
The special thing about ground source heat pumps is, well, that they use ground instead of air - and it turns out to be a really important thing because of the temperature differences between ground and air.
A/C or heat pump efficiency is directly related to the temperature difference over which you're trying to pump. If the temperature difference is twice as large, you need to spend twice as much energy to pump the same amount of heat.
Furthermore, the days where you need a heat pump (or A/C) the most are the peak cold/heat days where the temperature difference between your house and the air is much larger than usual. Because of this, a ground source heat pump can do the same thing by spending much less power than an air source heat pump, so it is "greener" - though the installation is more cumbersome and expensive.
However there are air heat pumps which differ from the AC ran in reverse only in how the heat is distributed around the house. For example with warm water in the pipes not just blowing warm air around.
There's no refrigerant here. Our heat pump uses plain water mixed with an anti-freezing agent. Just like the cooler in a car does. And there are control displays where you control all operating parameters.
As for the "pump heat from here to there" ... while we are cooling we are warming the ground below. And as at our place, the ground's consistency keeps the warmth rather local, we reuse it later when we warm our water during the night.
We do live in a densely populated area and about every fifth hoiuse built here during the last 10 years uses a ground-based heat pump. As for electricity use: each house has two hours of "blockage" where the pump is not allowed to run, so that the power lines aren't stressed. That's no problem at all, because all houses are highly insulated and thus buffer rather good.
That's correct. I was comparing our system to existing systems which directly use a refrigerant sent into the ground loop. Our heat pump itself is a closed system just as a refrigerator, and works indirectly via the water cycle used outside.
Is English a second language for you? I ask not because I am trying to insult, but what you are describing is just called geothermal heat in North America. It can also work in reverse if the air temperature is higher than the ground temperature.
Also, you have your units wrong. Electrical demand is measured in just kilowatts (kw). Actual usage is in kilowatts-hours (kwh) which is just an unusual way of saying joules.
Units are fine. He just said he gets energy as heat in the amount 4 times higher than amount of electrical energy he uses to get it.
It's fine to talk about it in terms of energy as it would be to talk about it in terms of power.
And I'd argue that kWh is exactly the usual way of saying 3600000 joules.
Also name "geothermal heat" for ground heat pumps might be a local US marketing term. In international English geothermal means rather what Iceland is mostly doing. Pumping water into very hot rocks deep below to extract heat. And it doesn't work in reverse because it would be additional work to pump heat into very hot rocks instead of dumping it into the air or into the cool ground 2 meters below the surface.
Geothermal works with either vertical holes in the ground or a big loop spread out horizontally. Neither one is very deep nor does it involve hot rocks.
Energy is specified in KWh here, i.e. we have a metering system installed which states that our heat pump delivered 128024 KWh of heat and the electricity company's metering system tells me that it used 34844 KWh of electrical energy to do this.
Anyway, for one unit input we got about 3.6 units of output, which has been produced with an almost zero carbon footprint, as we buy only ecologically produced electricity.
How does a meter compute delivered heat? Computing delivered electricity is easy, but to compute heat delivered you'd need to have adiabatic walls surrounding your house or something like that.
> Airflow based heat pumps are less efficient, and more noisy outside, of course.
This is only true when the ambient temperature dips below the geothermal temperature which depending on your location should make you prefer one over the other.
Germany. Where temperatures dip for some months below the geothermal temperature. Efficiency of air based pumps drops markedly when temperatures reach below 0 degrees Celsius.
And last but not least: ground / water carries much more energy per volume unit than air does. So air based heat pumps would make more sense in Europe's south and less sense farther north.
Modern water/air heat pumps have surprsingingly high efficiency down to -20C. We're running a 10 year old model that has no trouble heating our house down to -12, after which a direct electric helper element kicks in.
We did have no problems as the ground below consists mostly of clay for at least 100 meters. Two times at 60m was a political limit 10 years ago, because at 100 meters "suddenly" mining rules applied.
The tubes are about 100 mm in U-form, drilling mostly is offered in combination with the heat pump. And costs where payed of after about 7 years.
Costs and problems depend on the ground's structure. When I talked with the guys of the drilling team, they told me that problems occur if they work in hill regions with cavernous spots in the ground. That's because the tubes need firm contact to the ground to transfer heat.
Edit: here's an image of the drilling machine in operation: http://www.cynix.net/2008/img_1757.jpg and the tubes are those black ones on the rolls in the front.
Yes, air-exchange heat pumps have been around forever. But they're usually of the all-the-way-on or all-the-way-off type in the US. Newer systems use variable refrigerant flow and variable fan speeds to save energy, so they run more proportionally to the heating/cooling load. They have a higher up front cost so production builders don't put them in, but custom home builders will.
In cold climates you eventually hit an efficiency wall with the air-exchange units and need to use a ground-source heat pump, with glycol pipes being run deep in the ground to exchange heat. And/or also have a supplemental source of heat that only comes on during the very coldest periods (oil-fired furnace, natural gas, cast-iron stove, or even resistance heat).
In hot climates you can increase the efficiency of a heat pump by adding water mist, making it a hybrid swamp cooler. Evaporating water will take out a bunch of heat energy.
As was mentioned, insulation is key otherwise you're just spending money on heating or cooling the outdoors. Walls, door, and windows that don't have thermal bridges, controlled air exchange with the outdoors (ERV energy recovery ventilator units), and so on.
Compressors (the biggest power usage in an A/C) have gotten more efficient, plus they remove the fans in favor of dumping heat straight into the ground. That's about it, it's still basically an A/C unit.
This is old technology, I'm surprised the US hasn't already implemented it.
They have been remote-controlling water heaters in New Zealand and Australia since the 50s. Just a simple relay installed in each house that responses to extra frequencies on the power lines in the 160-1600hz range. It's called ripple control, for obvious reasons. Each home gets assigned to one of several channels in each area so they can have more fine grained control of the load.
About half of the US uses natural gas for water heating - its substantially more efficient than burning said gas (or coal) to generate electricity, then using the electricity to heat water.
> its substantially more efficient than burning said gas (or coal) to generate electricity, then using the electricity to heat water.
While this is true for basic resistive electric water heaters it's not for modern heat pump water heater which have energy factors of 3.5x which more then makes up for the 34% efficiency of a simple gas power plant (more modern combined cycle plants are 50-60% efficient) and the 95% efficiency of the grid.
Still works out much cheaper to use gas than electricity for heating in California with gas at $0.06/kWh vs $0.26/kWh for electricity.
Is it though? It might be cheaper in many area's but this source [1] says that the grid transmission loss is only 5%.
Am I missing something that makes it a more substantial difference?
Not to mention that piping all that natural gas out to each home has to result in a certain amount of leakage and energy cost in just the pumping itself.
Yes, even the most efficient natural gas plants aren't going to come close to the efficiency of a modern condensing gas water heater. For the water heater it's just a matter of a single heat exchange process from the exhaust to the water. For a combined cycle power plant you're dealing with a gas turbine and boiling water to run additional steam turbines but in the end converting heat into mechanical energy is not tremendously efficient.
Figure on the order of 60% efficient for the best natural gas power plants vs. 95% efficient for a condensing gas water heater. Not to mention the drastic reduction in expensive electrical infrastructure, the power plant, etc.
Gas to electricity efficiency is low so you loose more then half the energy when producing electricity from gas. Using a 90 percent efficiency furnace to heat water directly with gas is the better solution.
That's what I've seen. Heat pump water heaters cost about the same to run as gas units. And yes the advantage is they don't fundamentally use natural gas so they are 'green' as the grid they are tied to is.
However if you heat with heat pump you are getting more than 3 times more heat than electrical energy you used. So despite getting only 0.5 energy by turning gas into electriciy you are getting 3*0.5 = 1.5 of heating and you could go in reverse and get the cooling when you need it.
If you have a gas line to your home the most efficient way of heating would be to have co-generation gas turbine than makes heat and electricity and then use the electricity produced to power heat pump.
A lot of people also use fuel oil for heating (I know we did growing up in a suburb without gas lines). Someone comes by occasionally and delivers it. I expect electric water heaters are very uncommon.
I have a tankless hot water heater system in my new home that runs on a city natural gas line. It’s super efficient and thus my energy bills are very low compared to what I used to pay for the traditional electric hot water heater in my previous home, however it’s not a silver bullet. I find myself running the water for a ridiculously long time in order for the water to start getting hot, sometimes for more than a minute, depending on where I am in the house (obviously the farther you are from the heating unit, the more time it takes for the hot water to travel to its destination). Our water consumption is therefore quite a bit higher, thus I am not confident this is a good ecological or financial tradeoff. I have used similar systems in Europe and they seem to be a little quicker, but that could be from higher water pressure. They seem to suffer from the same problem though. Perhaps a good solution would be to have a small (4-5 gallon) booster tank that is periodically heated like a traditional tank-based system, so that when hot water is run, it can immediately be delivered while simultaneously engaging the on-demand system. Forgive my layman’s terminology, I’m not a plumber or HVAC engineer, but hopefully the idea is clear.
The majority of your savings are from switching to gas from electric. Gas is significantly cheaper per BTU. Gas tank heaters are still pretty efficient. Especially if insulated.
First, a gas-fired power plant converts about 40% of thermal energy to electricity, discarding 60% to further heat the planet. Then a few more percent are lost in transmission lines and voltage-lowering transformers. Only then that electricity is used to heat water or air in one's house.
If you just directly burn that same gas in the house to produce heat, it's nearly 3x as efficient.
If you use the electricity to run a heat pump you can get a couple more Joules out of the gas. Ideally your gas-plant is also connected to a district heating network, so the 60% heat are not completely lost.
A thought occurs to me just now: Why not also use that 40-60% waste heat to drive district cooling during the hot season? There's the absorption refrigeration cycle[1], which requires only a a heat input to drive the cycle to pump heat from the cold side to the hot side. Is the difference between the coefficient of performance between the more common vapor-compression cycle and the absorption cycle such that it is more cost effective to use the generated electricity to pump heat out of conditioned spaces during the hot season?
Both cycles are limited by the same fundamental value (the Carnot coefficient) so I don't think that it would be a huge difference between the two cycles. Rather, I suspect that there are not all that municipalities that have (or need) both district heating AND district cooling. I expect that in the future we'll see a lot more industrial use of waste heat from power plants though, and part of that might take the form of on-site absorption chillers.
In a post parallel to yours, lmm says that gas-powered plants are low efficiency. Can either of you supply some documentation or references for your respective positions?
I wonder what kind of thermal electricity generation achieves efficiency above, say, 45%. Efficiency of thermal engines, even when you recycle the waste heat of the gas turbine exhaust with another cascade using a low-boiling substance and another turbine, is limited.
I only mentioned the gas-fired power station to make it an apples-to-apples comparison. It would be hard to compare e.g. to solar panels, even though direct hearing by concentrated sunlight might be feasible.
Using gas generates fixed additional costs though, apart from the energy price. You have to pay an additional provider fee, the annual maintenance of the gas heater, regularly change the CO detectors, etc.
It's worth it for a larger volume though. Not so much for a small flat.
I had a friend who spent months measuring the power output of all his appliances and lights trying to figure out where half his electricity bill was going. He finally realized it was the hot water recirculator.
We have an under-sink unit that has hot water ready 24/7. After hooking it up, I noticed it increased our monthly bill by about $15.
I bought a used Wemo plug for $10 and set it to only be on for 3 hours in the morning and 3 hours at night. Now we have hot water at any of the times when we actually would want it, and we aren't wasting money/energy to keep hot water on tap 24/7.
> He finally realized it was the hot water recirculator.
The problem is using devices that are either timed or (even worse) just runs 24/7.
Ideally you'd want one that runs on demand when triggered by a switch: hit the button, it runs for 30-60s while you undress, and then we you turn on (e.g.) the shower the water is already hot.
The hot water supply for the shower should be the same as the sink, and so when you go to shave or brush your teeth, that's then already primed as well.
Do a search for "Gary Klein", who has written a lot of designing good hot water systems over the years.
We have a solar (parabolic vacuum pipes) water heater which provides 95% of our annual hot water needs, backed up by gas.
The heat is stored in a layered and heavily insulated 300 liter tank.
The water delivered to the tap isn't actually from the tank, but it's just fresh water heated instantly and on-demand through a heat exchanger which is part of the storage tank.
No need to worry about stale hot water with such a system.
They are not closed loop, they just push some water from the hot water line back down the cold line, where it will wind up back in the water heater and be used. They are no more prone to disease than you existing system.
Its worth noting that you can combine an on-demand (tankless) hot water system with at tank. The on demand system heats the water and stores it in the tank (which is not a water heater). The tank itself, since it has no heating elements, can be _very_ thermally efficient. You get the benefits of both systems (though it does cost more to install, obviously)
There are electric instant hot water systems available. The sink at my office only has a cold water line plumbed to it and a small black box heats the water right there. I've seen some in kitchens for making things like soup or coffee real quick. Not sure why they're not more common, maybe reliability/flowrate/other cost issues?
They need power and produce some noise. They take up space which may be at a premium. They require yearly-ish maintenance (running a cleaning solution through them with a small pump).
My parents got a heat pump water heater (electric) a few months ago and it's great. Definitely the priciest option, but it sips electricity and also cools the area around it (basically operating as an "inside out refridgerator").
In this same remodel I also convinced them to get heat pump / AC combo unit to replace the old gas furnace. Again amazingly cheap (even compared to gas), but also higher upfront cost.
This is in a coastal California region, so I'm not sure how well these heat pump solutions will work in colder places (ice would likely form on the heat pump near freezing, limiting its capability), but if anyone is looking to upgrade either a hot water heater or an AC unit, I cannot recommend the heat pump option enough (if you can get through the higher up front cost).
Definitely works in cold areas. Most heat pump manufacturers offer separate models for cold climates below zero.
The worst case is efficiency approaches resistance heating at 1.0, maybe with backup resistance heat strips. But a well designed system to match worst case load should rarely see this.
For some reason they've really only been widely available in the US in the past few years.
> But a well designed system to match worst case load should rarely see this.
Well actually it'll see it quite often. Every time a heat pump goes into defrost mode it'll use resistive heating inside to hold over while it's working like a traditional air conditioner to thaw out the outdoor coils.
Leaking coolant is a major problem. The standard for most small heat pumps is r412a and it is problematic.
To make the installs cheap, these systems use flare fittings that almost all seem to leak. Couple that with the fact the 412a systems run at high pressure and you get a lot of leaking refrigerant.
No HVAC techs I’ve met like the 412a systems and most seem to be hoping for more sanity from r32, though that will have its own set of problems (flammability)
A system like Sanden CO2 or Chiltrix will heat your water with outside heat, so it's always 2x+ the efficiency of resistance heat. If your climate is predominately hot then thermal collectors are far more efficient, but interior hot water heat pumps would be an okay choice where that's not possible.
I live in a cool place. This winter we had extended periods of -20C. Heat pump efficiency drops, but still stays above 2. SCOP (for year round average for heating coefficient of performance) units sold now are better than 5.
Also, if you are worried about the refrigerant leaking, you can sacrifice a little bit of efficiency and buy a unit using CO2 as a refrigerant with a GWP of you know: 1.
I think the biggest problem here for leakage are random construction dudes cutting the pipes when they demolish or remodel homes. If only they could gather the gas in the outdoor unit before, all of it would be saved.
If the hot water heat pump is a single unit (which is the vast majority of residential installations) and indoors, it is just stealing heat from your regular heating system. You're paying for that heat, so you aren't getting COP > 1.
Hence the preface of "cold area", but my heating season is over 6 months. The ROI is already long in HWHP even assuming the best numbers, and often negative once you account for reality in areas which get cold.
Who has that, a "indoor heat pump"? That's just stupid. Sure, exhaust air heatpumps "use" the (excess) heat from indoors, but that would just get expelled anyways.
Right, I stand corrected. I had never seen such a heatpump (based in the nordics, that concept would never fly), and I'll agree with you that in homes heated by "regular means" (resistive/electrical, fossil fuels) they add little to no value, simply adding complexity. In heating season they would just siphon heat energy from the rest of the house...
(They would however de-humudify the space they are in, but that's another thing...)
I'd argue that every house that has any sort of ventilation, even naturally aspirated ones, have excess heat in that any amount of air leaving the house "unreclaimed" while there is any heating need contains wasted energy.
Heatpumps using that energy are very prevalent in the Nordics and Scandinavia, even with a majority of the time being heating season here.
Nah. It does not necessarily have to be an air-water heatpump either, colder climates more often use geo-thermal or ground-water loops as the energy-well. Then the surrounding climate have much less of an impact.
Refrigerant leaks are still an issue though, but moving to hydrocarbons and CO2 will mitigate that.
Even R32 is a step up in that regard.
I looked at heat pump water heaters several years ago. They are massively expensive, have a little more risk of failure (potential for expensive repairs), and in many cases would only work for half of the year (basements are a common location and get relatively cold in the winter). I like the idea, the the ROI just wasn't there given the low cost of electricity, which green energy will continue to drive down.
I don't like the idea of the grid or cloud controlling appliances in my home. If I could program the run options myself based on the power company's recommendation (like a programmable therostat), that would be better in my opinion.
Not sure what a cold basement has to do with it? You suck in air from outside, extract the energy, and blow out colder air. The warm water is stored in an isolated tank (sure if the basement is cold it might cool off slightly quicker, but you warm up the cold basement which is a good thing). It is then used for heating the house via radiators as well as for warm tap/shower water.
We use it to warm a 240m2 house with four inhabitants. It works well down to -10 to -15C.
During the night we pay only have the price per kWh to the utility company (as they have excess capacity during that period).
It works great and it pays itself back quite fast.
It's not controlled by any cloud. You can regulate on the control panel how and when you want it to run and it adapts with the weather too if you want.
If your refrigerant can reach -20 in your system, and it's 30C outside, then your refrigerant is exchanging 50C of energy per cycle. But if it's -15C outside, the best you can achieve is 5C of energy exchanged per cycle. And at -20C outside, you can't exchange heat at all.
That's a bit hand-wavey and not exact units, but I think it accurately describes the problem.
What the above poster is saying is that as temperatures drop, the system gets less and less efficient. For some environments, it may become cheaper to use resistive electric instead.
That is why they are hybrid heat pump water heaters. When the air is insufficiently warm to heat your water, the heat pump can switch back to traditional electric heater rods.
They do run about 2x the price of a non-hybrid (My local hardware store has an 80 gallon hybrid for $2250 vs $1080 for the non-hybrid) but my power company is offering a $500 instant rebate as well as the county offering a $300 rebate, so in my case, it's a few hundred extra bucks for a few hundred dollar annual reduction in my power bill.
Wow 80 gallons is huge. I can see it making sense at that volume.
I find the benefits to be marginal when using an average 40 gallon or less and only using it for 1-2 people. The use of water conserving fixtures further reduces the benefits for smaller tanks with fewer people (not sure they even make them smaller than 40 with the heat pump). With the exception being for people in hot climates with the tank in the garage or similar space.
"Not sure what a cold basement has to do with it? You suck in air from outside, extract the energy, and blow out colder air."
The water heaters I saw were not running ducts to the outside, they use the room air. The point is that heat pump efficiency is tied to the ambient temperature. The hotter the air, the easier it is to collect the heat from it. So when it gets cold enough the "emergency" or "auxiliary" heating coil starts to be used (resistance based). This is very common in cold climates. My house heat pump auxiliary tends to kick in when the tempature gets below 40. This would also apply to water heaters if using outside air than the warmer basement air. Of course you are heating that basement air with another source, so that efficiency should be evaluated too (likely a heat pump because if you have a gas furnace, one would be likely to have a gas water heater too).
"It's not controlled by any cloud. You can regulate on the control panel how and when you want it to run and it adapts with the weather too if you want."
The proposal in the article is that smart water heaters could be controlled by the utility companies.
"It is then used for heating the house via radiators as well as for warm tap/shower water."
That is one type of system. The article is talking the US, in which the type of system you describe is relatively rare. The 10 million annual water heaters they reference are overwhelmingly used just for tap/shower water.
A good example of a government doing something that worked is the Australian government which wanted to spend money fighting the global financial crisis so insulated homes. Unfortunately deaths from the scheme, which were at the same rate as normal but became larger in number stop people talking about it much.
This tale of heat pump water heaters stopping a dam is rubbish. Where is the mathematics?
The one you reference is a very poor example of pumped hydro. It's nameplate capacity was only 30 MW, it was uneconomical to operate, and was dismantled in 2016.
1. heat pumps rather than resistance heating: move the heat where you want it instead of creating it from scratch.
2. timeshifting electrical load. Figure out how to add and shed it on demand.
The second one has a remarkable property. Load can be shed much more quickly than spinning up peak-load generators. That means grid operators can, in periods of overload, keep the grid's AC frequency (50 or 60Hz) from dropping. Without load shedding it's done with expensive and dirty peak-load generators. That's called "frequency control ancillary services" (FC/AS) in the grid biz, and it's economically important: regional grids don't work properly unless their local grids all run at the same frequency. Local grids don't want to be disconnected from regional grids in peak-load times because their generators slowed from 60Hz to 59.8Hz. Remotely switching off a mess of hot water heaters is a GREAT way to change the grid load quickly if that starts to happen.
Virtual battery, there is an interesting project to do a similar thing with aluminum smelters where you heat them and operate at full capacity off-peak and then during peak electricity usage you run slower. Since a smelter consumes so much power this can significantly level the grid usage.
Would that be economical? Places with abundant geothermal power like Iceland are probably going to make much cheaper aluminum smelting than anywhere else.
Usually its done with standard hydropower not geothermal, lots of aluminum smelting in Quebec. China produces like 10x more than the next highest producing country.
Not all thermal energy is created equal. The temperature level plays a huge role, and I imagine geothermal is on the low end. Suitable for household heating and the like, but not for smelting metal. From hydro, you generate electricity, and that can be converted to thermal energy on very high temperature levels.
I have worked in an aluminium smelter, given the heart stopping magnetic fields, toxic fumes and potential for explosion when even a small amount of water gets in I can say I really don't want this under my house
Not sure there's currently any sane way to put that into a house -- the industrial process involves a hydrogen fluoride loop. It's a interesting idea though.
Can you also store cold cheaply? For example, to run an A/C early in the morning, and put the cold in an insulated tank of a room-temperature phase change material [0]?
This is why old buildings in the Middle East and North Africa have thick stone walls. In these arid regions there is a large temperature difference between day and night, so the thermal inertia of the building can be used to store the 'cold'. Structures such as windcatchers help to naturally ventilate the building at night.
A long time ago I read an article that made an impression on me. This guy had developed a house using logs that were basically phase change material. I think part of the design was to build almost a house within a house. An inside wall made of the logs containing pine sap that would change phase at a comfortable temperature. So with sun it would reach that temperature then start absorbing it and becoming more liquid, then later slowly solidify giving off heat.
Most newly built electric cars have a 50+ kWh battery. Imagine if smart meters could use _that_, regardless of where the car is currently parked and plugged in. 50kWh is in excess of what most households use in electricity on most days.
That many cars seem undesirable in urban areas (or anywhere, really, but let's not go there).
From a bit of quick searching, EV battery packs are roughly the same volume as a fridge, and weigh in around 300kg (that was a Nissan Leaf specifically, but I assume others are similar). I don't have enough room for a fridge sized battery in my house. It'd be nice if they could shrink a bit. With enough capacity to run a tankless water heater for the duration of a nice, hot shower. The battery can charge slowly whenever power is abundant.
The grid doesn't care about running a bunch of laptops. But a bunch of tankless water heaters quickly add up. Having a local buffer really makes sense there.
On the other hand, if every home had a load leveling battery system of even modest storage capacity, say, 15 minutes average power usage covered, then load leveling would not be nearly the problem it is today.
You're probably right. Something like a small battery per home, and a bigger battery per block would likely go a very long way in creating a more stable grid. That's probably cheaper than "real" grid scale storage. What would a 15 minute battery look like? Probably not much bigger than a car battery. Install one with every power meter. Sounds so easy that I can't help but wonder what the catch is. Why aren't we doing this?
This will be the case in the next couple of years. Wall boxes are inherently smart (that is, controllable). So as a sink, the concept works somewhat already. But most cars won't be empty all the time. Also as source the 50kWh will only be usable as an emergency backup for the owner of the vehicle and only if they have the infrastructure to consume directed current. No one will let their own battery drain for the greater good. For public use cases people won't offer to unload more than maybe half of the capacity, realistically maybe 25% on average.
> No one will let their own battery drain for the greater good
Agreed. That’s why you‘ll get adequately paid for the energy sucked out of the battery in the evening when everybody starts cooking and energy prices on the market spike.
The big problem we have right now is that we want to get rid of coal and gas, but they are currently absolutely necessary for serving peaks occurring when wind power and solar lie flat. Vehicle2grid could be the solution - a giant distributed battery. I think if you charge 40kWh in the day with cheap solar, and sell it for 5x the price in the evening or morning, that would more than offset the battery degradation (which is way less of a problem than initially suspected, especially when charging and discharging slowly). A big battery could make you a couple of bucks every day.
Yes and add to that the ability of many of these large-battery vehicles to self-drive. For example when the owner is working during the day, the vehicle could drive to a regional charging station. This could help with the distribution component e.g. in rural areas with no power lines for the last few miles — the vehicle simply drives the power from where it’s available to where it’s needed.
We don’t use electricity for heating (heating and warm water are powered by community heat), and need 11kWh per day on average, excluding the EV. The EV adds another 5.5kWh per day.
My main consumers are probably the fridge and the oven. I made sure to buy an efficient fridge. Other than those I usually only have a laptop or two running. The washing machine only runs once or twice a week, most of the time only at 30°C.
Lots of good discussions about water heating in this thread. But it's such a tricky topic.
Tankless water heaters are pretty efficient, but when you need hot water, you briefly use huge amounts of energy. It's for this reason that they almost always use natural gas. Electric tankless heaters are a great way to cause brownouts. They're roughly the size of a microwave oven, so they can fit in pretty much any kind of dwelling.
Water heaters with tanks, on the other hand, take up huge amounts of space and require frequent (but lower) energy input. This can use heat from a variety of sources, including low quality/unrealiable heat sources like solar heat pipes.
Then there's space heating. Unless you live in a Passivhaus, keeping a comfortable indoor temperature is challenging. Central heating using hot water and radiators is the most common approach where I live. But this again relies on burning hydrocarbons. Or, increasingly, on heat pumps, which require a lot of space, are noisy, and drop in efficiency as the temperature drops.
As far as I can tell, there are no silver bullets in either space heating or water heating. If you have a really big house, a big tank is probably a good solution for hot water. But living in a really big house is horribly inefficient in its own way. So I'm guessing that's not the greener approach. Living in a smaller dwelling is more efficient. But it seems there are basically zero good ways to heat small living spaces and hot water for a family of 1-2 living in small houses.
Tankless are also useless if you don't have perfect water, and even if you do you have to descale them every year. The calcium, iron, and others in your water builds up in the small copper pipes, and an acidic cleaner is required to remove it. If youve ever used a Keurig it's similar.
Propane water tanks are pretty bulletproof. Even with bad water they just truck, and require no electricity to operate, unlike some other gas appliances.
Where I live, tankless heaters are pretty wide-spread. They connect to 3-phase power supply, heating at a variable power level up to 24 kW [1]. They need almost no maintenance, nobody I know has ever descaled one. I think the better units directly run the heating wires through the water, so they do not calcify due to small surface area (or maybe the huge temperature gradient when operated breaks the calcification layer).
Usually you operate them until they break (maybe around 10 years), then get a replacement heater for like 400 €.
Here in Belgium, electricity metering is switching from merely "kWh/year" to peak power draw (kW). Running a heater at 24kW will become very expensive.
I've proposed this (water heater as battery) innumerable times here on HN. Glad to see it finally catching on!
You can do the same thing with the HVAC system. For example, when the sun is high and electricity is cheap, have the A/C cooling a large mass of stone or concrete. Then, blow air over it at night to keep the house cool.
The PassivHaus concept utilises a massive (5,000 gallon / 20k litre) insulated thermally stratified water tank as thermal storage mass, among other elements.
It's used to create zero-net-energy homes in Fairbanks, Alaska.
You are not the first to propose it, and won't be the last. It is obvious to any engineer who spends more than a few minutes thinking about the problem. It works in practice too, but the space needed means most people don't bother.
Solar hot water heaters are cheap and can easily be 50% efficient, beating the heck out of 21%-efficient mass-market PV cells, often even if the PV cells are driving a heat pump. Thermosiphon-type solar hot-water heaters don't even need a pump, just a super-low-pressure check valve. Less efficient, but maybe even better, are safer passively-cooled solar hot water heaters, which can be made out of cheap materials like plastics and cement instead of stainless steel, and don't require a temperature-limiting valve to keep you from scalding yourself.
However, even if hot-water heaters aren't where it's at, I think circadian thermal energy storage is a pretty big deal for demand response, and demand response is pretty important for the renewables transition—though not as essential as many claim. There's thermal-mass energy storage like the hot-water heater approach (and Trombe walls, and earth-berm walls, and several other possibilities), but phase-change storage like the ice-battery approach mentioned in https://news.ycombinator.com/item?id=27757018 allow an order of magnitude higher energy storage density and easier temperature control, and "thermochemical energy storage" (generally through reversible hydration of desiccants such as CaCl₂) potentially allows another order of magnitude density improvement over phase-change materials, as well as offering the possibility of thermally-driven air conditioning, humidification, and dehumidification, as well as greater controllability.
I have 1200w of solar panels hooked directly to the lower element of my hot water heater. I sized the element to match the source impedance of the panels in full sun. If you use a MPPT system you could get 50% more power in partial shade but panels were so cheap it was not worth the complexity. The top heating element is still on city power as backup but I rarely use it.
The water will get up to 80c on a sunny day, so it can store enough heat to last a couple days without sun. There is a mixing valve so the water coming out of the tank is mixed with cold to stay below 50C for safety.
Solar hot water panels would make 4x the heat for the same area, but are too complex and expensive to install. They need pumps, expansion chamber, control system, antifreeze, new larger hot water tank. They are too heavy to get on the roof by yourself.
My non-grid connected solar cost about $1200, and was easy to DIY. No $1000 permit needed since it is not connected to the grid. No moving parts and almost no electronics. House now uses only 8-12 kWh a day.
I think these water heaters in question are actually hybrid units. They cool the surrounding room to maintain a temperature set point. In some places, colder room air and thus more condensation is not appreciated.
A less-sophisticated approach is to put your tank heater on a timer. Think carefully before you do this. Does your tank heater have the capacity to keep the water hot for a full shower, until you’re back under the non-peak schedule? If it doesn’t, you’ll be the first to hear about it.
Man, let me tell you about my friend the Greeks. Any time they leave the house, turn off the water heater. Hotel: water heater is off until you ask. All because in the 50s (iirc) they incorrectly installed a bunch of heaters which exploded from overpressure. I'd be surprised if they have unusually high rates of Legionnaires'.
Granted, no mention of this particular cultural artifact. Global temperature warming was cited in some reports as part of the cause of these outbreaks. It seems that the bacteria really likes to live in showerheads, so especially older shower heads can accumulate legionella especially given commonly lukewarm temperatures. This creates a perfect storm of ideal reservoirs, protected, moist, temperature conditions and aerosolized distribution.
Yeah, timer or grid controlled water heaters are old and busted (especially with bacteria concerns due to a lack of in tank convection). New hotness are heat pump water heaters that are very efficient and can even add cool air to a conditioned spaces by their inherent operation. Electric vehicle charging orchestrated as large aggregate loads are what replaces “the humble water heater.”
Tankless heaters are great if you’re burning gas, but electric versions are wildly inefficient versus a heat pump and require very large circuits and service entrances on the load center/breaker panel.
> timer or grid controlled water heaters are old and busted (especially with bacteria concerns due to a lack of in tank convection)
This is literally the first time I'm hearing of this as a concern. Our local recommendations are to keep tank temperature above 70C and you should be fine.
My heat pump water heater is at 140F all the time, maximizing the banked energy. There's an outboard mixing valve to reduce this to a safe temperature in the house.
https://patents.justia.com/patent/20180290899 provides background on the topic. Keeping your hot water tank at or above 50-55C constantly is a reasonable mitigation, anything hotter can cause scalding.
You can't scald yourself with mixed water from the faucet unless you set the faucet lever wrong, so I've never had that issue. In addition to that, the recommended high temperature setting (I believe the recommended default setting on my tank is 60 C?) increases the amount of mixed water that you can use before depleting the tank, so even a smaller tank suffices for a person.
Heat pump water heaters do seem promising... But many water heaters live in cold basements...
Classic tanked electric is so cheap to make & operate, I have come to think they may always be with us. (Though certainly a heat pump water heater is an easy choice in the right climate)
"Cold" basements rarely fall below 50 degrees Fahrenheit/10C. There's plenty of thermal headroom below that for heat pumps to work. Heat pumps already work outdoors at below freezing. I don't think there's anything to worry about.
More of a problem is when your water heater is within your conditioned space envelope and in the cold months when you are heating your space the hot water heater takes that heat. Its not a huge issue but you do run the heater extra for the heat that's going into your hot water. If you've got an air source heat pump outside then its just an extra step.
I was thinking the same thing. You don't get something for nothing. Assuming the water heater is in the conditioned space, it will just make the central heater work harder (and consume more fuel) during the winter months. Maybe this is offset during summer months when it can help the AC cool the space.
None of this applies if the water heater is not in a conditioned space, but that's not feasible in (common) environments with cold winters.
Heat pump models usually have a resistive element for use when the heat pump can't keep up, or when the climate doesn't cooperate. Then you benefit from the efficiency whenever possible. (Here in coastal CA I have mine set to only ever use the heat pump since the climate is so mild.)
The up-front cost of a heat pump is definitely an issue. IMO we should be doing instant rebates to even out the cost between the two so that it's an easy decision.
Yeah, but only if it is flowing across the deposit.
If you do the "bare minimum 140f once a day" method, you have to flush all the hot lines with this for long enough to kill it.
All this also presumes correct thermostatic calibration and generally even temperature distribution in a system planned to age with minimal maintenance.
The process isn't instant, you also have to ensure the hot water hits all the lines down the way at the appropriate hold temp and, well, hold it there for long enough.
These outbreaks still occur today. Not a huge problem, but why design such a well controlled hazard back into your potable water?
Where I am, you’re not allowed to deliver water to fixtures higher than 49C (120F), to reduce scalding risk. and this is usually accomplished through a mixing valve at the hot water tank outlet.
11m people live here, haven’t heard of any evidence of increased legionnaires:
I have a few servers that I have in a rack in my basement for various projects and work that I do. I ended up having to cool it in the summer so I made a small room around it to limit the amount I had to cool.
When I replaced my water heater, I went with the hybrid model and dropped the AC. The room stays cool, my water heater uses less power on average and I don't have to fire up the ac unit at all.
Large insulated tanks of water are cheap. Sizing your house for a full week’s hot water is going to be cheaper than paying peak rates. That doesn’t help people today, but water heaters don’t last that long.
Alternatively a tankless water heater provides both redundancy and instantly hot water.
Large tanks are cheap, square feet of residential space are expensive. Tankless water heaters work well when powered by nat gas, but if you want electric it’s not great.
I’ve been intending to do solar water heating, and convert from gas to electric, but the old heater gave out at the wrong time. So the current plan is build the solar and make a new place to move the electric tank into, then use the other tank for extra storage of the solar heated water. The good news about climate change is that I never have to worry about the pipes freezing any more.
Climate change is making weather more extreme, in both directions. “Global warming” is a good descriptor of global climate as a whole but a bad descriptor of the effects on local weather. Many places are seeing higher highs and lower lows.
The only saving grace at the coasts is that you’re sitting beside a giant heatsink.
A family of 4 is normally fine with a 60 gallon water heater. Doubling that to 120 gallons takes up roughly 1 extra square foot of floor space assuming a 6’ tall tank. If you’re living in Manhattan at ~1,500$/sf might be worth it to avoid peak rates, but just about anywhere else it clearly is.
Climate change tends to mean more extremes, hot and cold (and windy). Southwest Canada is normally known for mild summers but it peaked over 110F last week. It was 95+F in my office.
I’m not sure if this is a stupid idea, but I think of all the energy people spend in places like LA to heat their pools even in the very warm months, while blasting AC inside. This seems like a pretty good opportunity for using a heat pump to take the cold pool water and use that as a heat sink for the hot indoor air. Or is there something about this setup I’m missing?
I used to work at place that installed this exact system. You can get an extra 2-3 months a year use of your pool in warm climates. It does work but we sold way more geothermal systems then these pool based systems.
Issues:
Building inspectors do not like it because it is non-standard. Copper is attacked by wet chlorine so you have to use stainless heat exchangers and plastic pipe. Pool filter must be constantly maintained to ensure the AC does not get clogged. If the pool is small, it can become very warm in august, almost like a hot tub.
Energy efficiency/load redirection is not the same as energy storage.
Heat pumps water heaters, with good insulation is about 3-3.8 times more efficient than straight electric heating. However keeping hot water hanging around isn't all that efficient.
Source? For solar heating you'll want one to store excess heat collected during the day.
With (grid sourced) electricity as the only energy source for the heat - and in absence of a "smart grid" - storing hot water adds losses, compared to heating the water just in time. So I can understand why they might think about some sort of ban.
If they go for a ban, I'd expect them to add some conditions.
I'm able to turn my water heater off twice a week without a noticable difference in the water temperature. I wish there was an easier way other than flipping the circuit breaker.
Good point. We can accomplish a lot in aggregate if we act together. Building codes and other regulations should be paired with financial incentives from government to accomplish energy goals like these and other climate goals. Markets are bad at solving this problem and we need to take some of the incredible wealth generated by those markets and in those markets to improve society.
It looks trivial if you've never done it. If you actually try you'll see that manufacturing a safe, quality product at scale while turning a profit is extremely difficult.
We used to be world leaders and we collectively decided it was better for a handful of people to be wealthy instead. Excess wealth (>1 billion dollars is a nice start) should be used to improve society in ways like these and in many other ways. A society is great when it solves problems, not when people are wealthy.
Hot water tanks are generally expected to last about 12 years. Some make it 40, but some die after 5. (replace your anode rod!) So we already make a lot of them.
What the enthusiasts for heap pump water heaters miss is the source of the heat they are pumping.
In the summer they are removing heat from a hot house, great - free air conditioning.
In the winter they are removing heat from a warm house, which then needs to be replaced by some other heating source to keep the house warm, great - you get to pay twice.
I tried turning the heat pump element on my heater off during the winter. However, it is programmed to automatically turn on again after 5 days.
That heat in the hot water is coming from somewhere, and you're paying for it regardless of where it came from. The question is _how much_ you're paying.
The magic of heat pumps is that in many cases, they can move X joules of heat by expending less than X joules of electricity. As an extra bonus, in the winter, any "waste heat" from the heat pump doing its work is still inside your home and not wasted at all.
So you could view a heat pump water heater as a way of converting one type of heating cost (the fuel/electricity used in a conventional tanked hot water heater) into another type of heating cost (the fuel/electricity used to heat your home).
As long as the cost of the electricity used by the heat pump is not astronomically higher than the cost of whatever is heating your home, it should definitely be in the green.
edit to add: Many state and local governments along with utilities are offering incentives/rebates/discounts to install heat-pump hot water heaters.
