radiant heat - balance points and remote control

PB_3

I am writing in search of a resource that might have some answers for me about radiant heating.

I have an existing house in Massachusetts with radiant heating (sub-floor, staple-up, PEX, 2" air space, 6" f-glass, a final layer of Astro Foil applied 90 degrees to joists). Walls and ceilings are foamed with Corbond. Finish flooring is wood in all rooms.

This house is a second/future retirement home. It is not used frequently during the winter months, perhaps 1 or 2 times per month. The house has 5 zones in 2500 sq feet. Thermostats (5) are currently set to 57 degrees.

It seems to make some intuitive sense to set the heat low while we are not there. That is, it must cost less energy to maintain a house (during the winter) at 57 than at 68.

Because of the nature of the thermal mass/radiant approach, getting the house to a comfortable temp requires about 8-10 hours. Although there are telephone controlled thermostats on the market, I have not been able to find any for radiant systems, probably because radiant is typically a set-and-forget system. We understand radiant does not typically respond well to the setback approach commonly used in radiator heating approaches. There is also the concern of cycling effects of cool down & heat up on the wood floors.

We knew this going in and fully expect to have the house set to one operating temp once we are there full time. Until then, we are faced with the warm-up period for our off-season visits. Of course, these warm-up visits are offsetting at least part of the savings of keeping the heat down.

What I am trying to find out is if anyone is aware of any engineering studies concerning heat recovery and questions like this:

1- What is the approximate additional cost of setting the thermostat at 68? (e.g., instead of 57) Are there any studies that have an approximate % cost increase per degree of temp rise?

2- Should the temp be even lower than 57 if we are not there but 1-2 weekends a month? Or, are do lower temps represent declining benefit in terms of the cost/comfort balance?

3- Is there some sort of "balance point" between energy savings and warm-up costs? For example, if it were to cost just 5% more to keep the temp at 63, that might be worth it if the recovery was cut from 6 hours to 2 hours. (which would also seem to cut warm-up costs)

I suppose we could just set the temp to 50 in November and not come back until May, that would be the easiest (and cheapest) approach. However, we do enjoy the house during the colder months as well.

One approach to getting some answers would be to spend the money to heat the house for a year and [after adjusting for degree days] compare to the prior year's costs (with low temp and periodic warm-ups.) Good as any approach I guess, just takes longer for the answers....

If anyone has any leads to some resources that might be able to help with these questions, it would be much appreciated.

Thanks very much.

Mark Eatherton1

Most tekmar controls...

come with an Occupied and Unoccupied setting that could be enabled and disabled from a simple dial up switch. The fuel saving for long term set back is proportional. The only caution I would give is that in turning things WAY down, you may be exposing the homes domestic plumbing system to a freezing potential. If you choose this route, I'd suggest you look into The Water Cop, and another device called a Low Temp Alarm.

As far as the cost of recovery is copncerned, it depends. If the house has a LOT of high mass materials inside, you could pay extra heating all that mass up, versus a low mass house.

ME

Uni R

Secondary Heatsource

Have you thought about a large high BTU oil stove or gas fireplace depending on your fuel? This could bring the recovery time down for key areas where you want comfort to a few hours or less.