I once had a new house with hydronic under floor heating - the worst heating setup I've every had - horribly slow to respond and expensive to operate. We turn down the heat to sleep and finally I just shut off the heat to the bedrooms and heated them a different way.
Our initial experience with the system was even worse than it might have been. The people who installed it including the thermostats were plumbers and did not realize there was a switch inside the thermostat to choose among three types of heating systems. They left all the thermostats at the default forced air heating setting. We suffered for two years with terrible overshooting and undershooting of temperatures before my own research revealed that the hidden setting existed and that it was set incorrectly. This helped but it was still not great.
We were glad to get back to a forced air heated house. I do believe however that hydronic heating with radiators is somewhat better than underfloor hydronic.
What you call a hydronic under floor heating can be a very good system if done properly. It is called low temperature underfloor water heating where I live and pretty much everyone puts them in newly built houses. Here usually there is a panel on every floor with mixing valves that set water temperature for the floor and flow on a per room basis. I can see however how it can be bad trying to heat up an older less well insulated house.
My underfloor water heating is powered by a wood pellet burner. The house is very well insulated so the burner is off May till late October. The burner has an outside temperature sensor and since it was initially set I haven't really had to mess with the settings beyond testing how to change it. The temperature in the house is pretty much constant 21C or 69F during the heating season. If I want to change it the response time is around 1-2 hours so although I don't use those settings one can imagine programming it for 5 degrees lower when you're at work and for it to bring up the temperature to the normal setting before you arrive.
As for the cost, I have a rather small 3 bedroom detached house (110 sq.meters or 1185 sq.feet), I live in a climate where we have -20deg.C winters (eastern Europe) on top of a rather windy hill, and I pay around 460 Eur per year for the fuel for the burner. I usually burn 2.5 tons of it. This is only to heat the house. Water heating for shower use etc uses electric on demand heating. Compare this to when I was living in a city in the north of UK, so much milder climate, in a 2 bedroom semi-detached house smaller than my current house with typical central heating (or what is called hydronic heating here) using gas fired burner. I would pay around 700-800GBP so almost 900EUR per year of heating so almost exactly double. I realise I'm comparing here two houses built 50 years from each other, but the UK climate is much milder and the older house is only semi detached. This should work in its favour. Still I spend half of what I used to.
I wonder if better PID tuning would help, maybe adding stuff like ambient outside temperature or weather prediction as a system input.
I know the nest thermostat does a lot of systemic learning and understands the outside temperature. (I'm not recommending that system, just that a little modern control theory might make things workable)
I have a 2nd gen Nest thermostat since they first came out in 2012 or so with a hot water system, so I can speak from my experience.
There is a setting on the thermostat (True Radiant) that takes into account the long heat-up times of radiant systems. With this setting off, overshoot is real. On cold days, True Radiant does start the system earlier. For example, it take about 2-3 hours in the deep of winter vs 30-60 minutes now.
However, it seems to be based to on a look-up table rather than an algorithm. It doesn’t take into account forecasted conditions, such as a temperature rise overnight, strong winds or decreasing/increasing radiance of the sun over the season. Those latter factors do make a difference in whether the house reaches the target temperature on time or whether overshoot occurs, and whether I am slightly uncomfortable.
As far as I can tell, there is an automatic set-back for heat pump systems. I wish this was given as an option for manual scheduling in True Radiant mode. To this day, I can’t tell whether there is an effect on efficiency (based on run-times which the thermostat dutifully displays).
I also wish the thermostats (in a dual-zone system with a single boiler) be “genlocked” or run on common firing times with demand prediction for temperatures to make use of boiler run-time, rather than running the boiler just when there is a request for heat in one zone.
I thought all heating systems had outdoor input for temperature. I know all houses I have lived in has had that the last 40 years at least. But I live in a cold area so I guess that's different. -38 C is uncommon but happens now and then. Also the isolation of the houses are better and that also helps with leveling out temperature differences.
