Radiant heat night set back? 1

[user007]

I have a 'large' house with about 4000+ sq ft of radiant heat on my first floor that uses stadler heat panels with pex tubing run in them (low mass radiant). I also have a huge basement (4000 sq ft, all unfinished space) that has pex tubing, manifolds and copper pipe running all over it to get to all the different zones in the house (carpet, wood, tile) with a lot of heat loss in the basement. I have been running this system by setting the night temperature back to 60 degrees and then starting the radiant heat at 4:30 am to start warming the house up again for 7 am wake up.

The radiant heat people I have talked to say to not set the heat back at night. Several mech. eng. professors say that setting it back is the right thing to do.

There is a large amount of heat wasted in the basement getting the system back up to temperature in the morning and I am wondering if by cycling the radiant system off/on like that I am actually using more energy than keeping it at temperature all night.

I look at the radiant panels as a large capacitor that needs to be charged before heat gets into the living space. I also look at the basement where heat is being wasted as another large capacitor that needs to be charged before the heat gets into the living space. I am wondering if I waste more energy charging these capacitor every day at start up than just keeping them 'charged' by keeping the heating system on at night. of course, both capacitors are 'leaky' capacitors so keeping them charged requires energy also.

so, I am looking for opinions on keeping a low mass radiant heat system on all night or using night set back like I have been doing.

thanks for your help. if this is the wrong forum for this please tell me and I will post at another spot

 

[GMcD]

I'm not clear on whether the basement has embedded PEX in the concrete or not? Is it just the Stadler heat panels in the main floor that you are questioning? Are the distribution pipes serving the radiant system insulated or not - or just running in the open in the unheated basement? Is there insulation below your main floor separating the heated floor from the basement?

The rules of thumb as a starting point are:

For low mass/quick response radiant systems it is OK to use night setback. For high mass radiant systems with a very slow response, DO NOT use night setback- the thermal inertia will use more energy cycling than the constant flow (or even timed intermittent flow) with variable temperature.

A high mass radiant floor system is anything with more than 1.5" of concrete/gypcrete. The thermal response time of concrete is about 2 hours per inch thickness, and is also dependent on where the PEX tubes are relative to the controlled surface.

 

[user007]

Thanks for your reply....Here are answers to your questions-

there is no pex in basement floor. all pex is part of first floor stadler panels which is what I am asking about set back about. pex and distribution system is partially insulated (please see my other recent post about that question since I have questions about that too). there is insulation below main floor separating living space from basement, but basement actually is warmer than the living space most of the time

In the other post, I am trying to learn how to better insulate the pex and manifolds to reduce heat loss in the basement

thanks again. I really appreciate your reply

 

[russmech]

The most correct solution would be to add insulation between the heat panels and the basement such that the (unwanted) heat flow to the basement is reduced

However, if that's not an acceptable answer, then it is more energy efficient to setback during the night than not setback.

The energy loss rate of a space (to the outside) is directly proportional to the temperature difference between inside and outside. The AMOUNT of energy is proportional to the length of time the space loses heat at that rate. So you will lose less heat overnight at a lower inside temperature.

Overheating the basement is an unfortunate result of the lack of insulation between your panels and the basement. However, if you keep the upper floor warm all night, the basement will also be at a higher temperature all night due to the same system heat loss from above. Therefore, the basement will also loose more heat to the outside.

The amount of insulation required to stop the unwanted heat flow is not much. I've read the R value of the underfloor insulation should be 4 times that of the R value of the flooring above the panel. So find the R value of all flooring above the panels, multiply it times 4, then add that amount of insulation below (use foil backed insulation with the foil UP to reflect radiant heat). Unless you have a heavy carpet pad with carpet over your panels, my guess is an R-3 or R-4 insulation would do a lot to alleviate your problem (I think that's about 1 inch of fiberglass insulation).

 

[RossABQ]

Russ is right on! I would add that it sounds like the furnace is also in the basement? That it probably the biggest contributor to the temp in the basement. Is it possible to recirculate some of the basement air to the upstairs? Even leaving a stairway door open would allow "excess" heat in the basement to go upstairs.

Is the basement externally insulated (foam around the walls, underground)? Many codes have required that for the last 10 or more yrs.

 

[MintJulep]

Russ is right. The only thing he neglected to mention relates to your heat capacitor concept.

The energy you put into the capacitor can only go to two places. Towards useful heating of the house, or to waste to the outdoors or ground. I won't go anywhere different because you turn the thermostat down. Whatever energy you put in in the morning when you turn the thermostat up comes back out at night.