Solar gain and cool down time causing problems

evanrmchugh

I am heating a 3400 square foot home with infloor radiant hydronic heating. The house has a south eastern exposure with multiple large windows and hence, a high solar gain during sunny days. It's not uncommon to see the thermostat in the main area climb from 21.5 (set point) to 25 or 26C during these sunny days, even when it is cold outside. The issue I'm experiencing is that in that situation, the thermostat will not begin to call for heat until late in the evening (then due to the infloor hydronic response time, will not warm up for a couple of hours), and while the room temperature doesn't typically fall below 20, the room feels cold because the heat hasn't been on all day, resulting in a cold wife and an uncomfortable room...lol.

On a secondary note, I believe my efficiency is suffering because most of the water in the system has a significant period of time to cool down and needs to heat all the way up again in the furnace during the call for heat.

Does the group have any suggestions or thoughts on how to improve this situation?

Hot_water_fan

On a secondary note, I believe my efficiency is suffering because most of the water in the system has a significant period of time to cool down and needs to heat all the way up again in the furnace during the call for heat.

No, your efficiency shouldn't change. Maybe if you have a condensing boiler that exceeds the condensing range during the ramp-up, but unlikely.

This is a common issue with high mass radiant floors - you have to bring the entire floor's temperature up and concrete is dense. One solution could be to add low mass heat emitters to the room for this recovery period. A panel radiator, baseboard, or hydro coil could all work.

Jamie Hall

Not an uncommon problem with spaces with a lot of sun exposure, unless the sun space is designed to be able to store the heat in something or circulate it -- even without radiant heat. May I presume you are using a space, not floor, thermostat?

There are two parts to this. The first one -- as you've discovered -- is to try to maintain the floor at a comfortable temperature, and for that you really need a floor thermostat. The idea will be to circulate warm water through the floor all the time, just warm enough to maintain the floor temperature at about 21 or so. You'll also need a mixing valve, and the piping for the boiler arranged for primary/secondary -- so that the boiler only comes on now and then to put some hot water into the system. Do not let that floor cool off!

Now. Second problem is what to do with the sun. Ideally the space floor coverings, if any, would be such that the sun would contribute to heating the floor. Otherwise... you're going to have to lose some of that heat somewhere. Is there any way you can circulate the excessively warm air to elsewhere in the building? Any ductwork and fans you could use?

evanrmchugh

Jamie Hall said:

Not an uncommon problem with spaces with a lot of sun exposure, unless the sun space is designed to be able to store the heat in something or circulate it -- even without radiant heat. May I presume you are using a space, not floor, thermostat?

There are two parts to this. The first one -- as you've discovered -- is to try to maintain the floor at a comfortable temperature, and for that you really need a floor thermostat. The idea will be to circulate warm water through the floor all the time, just warm enough to maintain the floor temperature at about 21 or so. You'll also need a mixing valve, and the piping for the boiler arranged for primary/secondary -- so that the boiler only comes on now and then to put some hot water into the system. Do not let that floor cool off!

Now. Second problem is what to do with the sun. Ideally the space floor coverings, if any, would be such that the sun would contribute to heating the floor. Otherwise... you're going to have to lose some of that heat somewhere. Is there any way you can circulate the excessively warm air to elsewhere in the building? Any ductwork and fans you could use?

I think you're on to something there. You are correct, I am using a space thermostat, not a floor stat. The entire space has ceramic tile so when the heat has been "off" for a period of time, the floor feels pretty cold and takes a while to warm back up. I need to do my research on how to best make that work, do you have any recommendations on floor thermostats?

Jamie Hall

Tekmar makes a good system, so I've been told...

Derheatmeister

As jamie said Tekmar may be able to "Help" a little with some of the PID controls they offer..I your case the heat may have to turn on hours prior to it actually being called for,hence the PID...IMO and in my experiance Radiant walls and panel rads may also help solve some of the Downward dips once the sun sets.

neilc

I know you said solar gain, but,
on a period of cloudy days, is the thermostat still on and off? alot?
are you running too hot a water and floor temp? that's cycling the thermostat?

Zman

Outdoor reset would make a huge difference.
Indoor temp feedback and floor sensors would help as well.
Tekmar can handle integrating these strategies.
As Derheatmeister mentioned, low mass radiant has the advantage of throwing less mass at the "Thermal Flywheel" and faster reaction time when the sun goes down.

How is your radiant constructed? Underfloor or in slab? What type of boiler? Is outdoor reset being used?

hot_rod

You need to be able to regulate the solar gain, any window coverings? They have motorized versions now that can react to the sun or temperature, also so glass that darkens to control the gain.

Zman

hot_rod said:

You need to be able to regulate the solar gain, any window coverings? They have motorized versions now that can react to the sun or temperature, also so glass that darkens to control the gain.

This is a great idea if you can swing it. We did a system where there was no AC but the motorized blinds closed automatically any time the smart home system was in away mode and there was a call for AC.