Dale

WayneMech

Dear Sirs,

     We're up against a church building committee that

says radiant heat is NOT more efficient than forced air and therefore

want us to rebid with forced air.  We need proof and numbers, maybe even

testimonial from other churches or similar places that show radiant is

more efficient.



     The radiant bid is for a gymnasium and maybe won't be occupied all

the time when first opened. We believe we can persuade the uneducated

committee, but as of yet are unable to get our hands on the information

necessary to convince them to pay out the extra money up front in

installation costs in order to save the money down the road on the

energy bill, not to mention the comfort factor.



     Please guide us to information that will give us the proof, numbers

and testimonial we need.

     Thank You.

     D&D

Jean-David Beyer

I am not an expert, but

At one time, someone wondered about converting the forced air heating system to hot water heat in out (almost) 200 year old Quaker Meetinghouse. While, in general, I would favor hot water heat supplied (when appropriate) by a mod-con boiler with outdoor reset, it seemed to me to be a very bad idea in our case, even though there are a few advantages.



The advantages would be less dust, quieter heating, and probably cheaper heating in a situation other than ours. Our building is two stories high, and heat might go to the top where few people choose to sit. If we put radiant heat in the walls, it might be possible to heat to lower temperatures. Our walls are heavy wood timbers with all the space bricked in. Outside walls are cedar shake; inside walls seem to be plaster.



The biggest problem is that the building is unoccupied for extended periods: often 6 days at a time. One room, with no plumbing in it, we allow to fall to 40F. The other room, with plumbing, we allow to fall to 50F. After that, it takes quite a while to reheat the building. It can take 10 hours with forced hot air because we can produce only 250,000 BTU/hour with our existing furnaces (125,000 from each of two). This much setback means a difficult time during recovery, especially for radiant in slab heating. We would not wish the pipes of the heating system to freeze, and air does not freeze in New Jersey. (In our case, it might even make sense to use a steam heating system.)



For us, the best way to economize on heating is to improve the insulation of this old building, and reduce the leaks, and install better windows. For historical preservation reasons, we cannot put in thermopane type windows, but we have started putting in storm windows (with something like plexiglass instead of glass).

CMadatMe

Wayne

Here is your answer to them. Heat loss...Heat Loss. Heat  Loss. You need roughly 35% less energy to heat a space radiantly than forced hot air or hydronic basedboard. Do the heat loss both ways. The proof is in the pudding...

NRT_Rob

Uh

where are you getting the 35% number?



I could model situations where radiant is LESS efficient than a well designed forced air system. high temp stapleup over unheated basements come to mind...



to the original poster: try contacting the RPA. they have all the final docs available on the subject. there were some poor studies that the building committee might be aware of that are causing the problem.

CMadatMe

We Are Not

Talking about system efficiency. We are talking heat loss. Set point and air changes per hour or "inflitration" when desiging a forced hot air system can account for an increase of upto 35% more energy needed to overcome that structures heat loss vs a radiant system. A radiant system air change per hour is much less as well as it's design setpoint.

NRT_Rob

disagree

good system vs good system and those numbers don't really have to change that much between radiant and forced air. Some, perhaps... mostly due to stratification... and a great reduction in distribution energy usage... but nothing like 35% in an apples to apples comparison.



studies do show that while there may be a theoretical case of lower setpoints for radiant, most people who get radiant don't turn down their systems. I don't recommend using that as a basis for savings claims. It's more of a comfort upgrade, on that issue, then an efficiency benefit.



and in any case, 35% is extreme. you could eliminate infiltration completely and not nix 35% of someone's heat load in most cases.

CMadatMe

I have a Question

What is the difference between a radiant heat loss and a heat loss for forced hot air? Do you use the same infiltration/air exchanges for both? What set point do you use for both types. I will empatically stand my stance on this and that comes through doing hundreds of losses.

NRT_Rob

you should know better

then to argue on the basis of having done "hundreds of losses". I've done a couple thousand easily and I've never undersized a boiler... so that means I'm still oversizing systems. Yet I'm still 20-30% under almost every other heat load I ever see.



Load calcs are important but they sure aren't exact.



I will restate that set point should not change. It does not change in real life, pretending it does only overstates the case.



The only serious additional leakage for forced air is duct leakage if you run it in unconditioned space and don't seal very well. otherwise it's neutral pressure on the house, it pulls as much as it pushes.



another point in the good system vs good system column: good forced air systems don't run ducts in unconditioned spaces.



Seriously. 35% is way out of bounds. That's "you replace a 30 year old poor system with a brand new advanced system" type numbers, not an apples to apples comparison with modern tech.

Paul Pollets

Radiant by Committee

I would do a heat loss analysis using the Uponor ADS software and a program for forced air design. The modern software is very accurate and takes into account the envelope design of the current building.  While gymnasiums are ideal candidates for radiant floors, ventilation is still required.

I've seen gym designs having 1-2 ACH vs a residential system with a code minimum of .35 ACH. Good software programs allow you to enter the infiltration factor and specify the ventilation requirements.

Uponor has done case studies and could help with the sale process, if you use their products.  They have a commercial division and have experts to aid the process.

I have seen radiant vs. forced air commercial comparisons that show a 35-40% fuel cost savings for the radiant in the NW climate.  The difficulty in "apples to apples" becomes bogged down in the cost of ventilation + radiant.

Didn't Dan H. once say, "Never work for friends, churches or synagogues. These jobs will never work..."

CMadatMe

Paul

Have done it using the ADS many many many times and it is generally a 35% less of a loss heating a space radiantly. The simple solution to the arugment is simply to run the Wirsbo House in the CDAM both ways. Which I think I will do.

Charlie from wmass

Burnhams hand book!

I know I read a comparison of forced air and forced water heating systems. I believe it was in the Burnham book. I am trying to locate it. The thing is it is comparing baseboard style forced hot water to forced air. When properly done even the lowly baseboard gets heat from the flame to the people more efficiently than air ducts can.

Unknown

Hey Charlie,,

I think you`re referring to Burnham`s Heating Helper.

http://www.usboiler.burnham.com/contractors/toolbox