[Greenbuilding] [BULK] controlling floor heat

[Keith Winston]

Someone else mentioned outdoor reset controls, which I don't know how 
you'd implement on the Takagi as it's doing double duty, but otherwise 
the outdoor reset idea can be good. And yes, your floor temp should be 
much lower, more like 100-110 probably, in a slab. It should reduce the 
amount of heat you're losing into the ground. But yes, you might still 
want to ditch the radiant, put some insulation on TOP of the slab 
(carpet? cork floor?) and use something else. Mini-splits are certainly 
an option. You mention air-source air-to-water heat pumps: do you 
actually know anyone that makes those? They are fairly few and far 
between, often called "chillers", rarely used for residential 
applications. I wouldn't be confident that they'd save you that much in 
fuel cost, unless you can get something with really high SEER.

Keith


Lawrence Lile wrote:
> Thanks, Niko.
>
> Yes, my slab is sitting on a gravel pad, only insulated vertically along
> the perimeter.  At this point I would not recommend that for any house,
> especially solar, and especially especially floor heat.  What you are
> seeing on the edges in the photo is the edge of a plastic vapor barrier
> - no foam.  Also you are seeing my lovely assistant Mrs. Lile, who is
> also not well insulated, thus the relatively high temperatures in the
> house.  
>
> You and I are in the same boat - bubble wrap is basically no insulation,
> just like I've got.  My heated floor is 1500 SFT, and the heat seems to
> drift up to the second floor regardless of the source - solar, wood, or
> radiant floor so I don't really heat the second floor.  Open plan really
> works for this. 
>
> It looks like I am starting with higher supply water temperatures than
> you are using (140F) - and I theorize that higher floor temperatures
> just toss heat into the earth more efficiently.  That may be one of my
> main problems after (D'oh!) no insulation. 
>
> I am using a Tagaki tankless heater for both floor and DHW.  The output
> of the heater has two thermostatic mixing valves - one set at 140F for
> the floor (Per The Radiant Company) and one set at 115F for the DHW.
> The way they are piped, the floor mixer being first in line, the DHW
> second, the floor heat can't be any colder than the DHW.  
>
> One idea I have is to replace the Tagaki altogether with a air source
> heat pump that produces hot water.  The Tagaki could do DHW service or
> serve as a backup floor heat when it is too cold outside.  (Or maybe I
> could sell it on Ebay!)  With a heat pump, I'd be paying 1/3 the cost
> for the energy for the floor, and probably supplying much lower
> temeratures to it, meaning lower heat loss to the ground.  
>
> One of my basic issues with Radiant floor, now that I think about it, is
> the radiant floor heat source really doesn't have much connection with
> the outdoors. Uninsulated slabs make this worse.  It will tend to
> produce a constant amount of heat, regardless of the outdoor
> temperature, and dump that heat into the ground, using up energy even on
> mild days. 
>
> Maybe I should just write off the Radiant floor as a bad idea badly
> implemented, and just turn it off.  I could put a heat pump on the air
> handler or install a couple of mini-splits and be done with the whole
> problem.  Hmmm....   
>
>   
>> I am in Vermont with a much cold clime than you
>>     
> in Misery (oops),
>
> Misery indeed.  Actually, I love to solve problems, especially this
> sort, so it is great fun.  
>
> Lawrence Lile, PE, LEED AP
> Project Solutions Engineering
>
> -----Original Message-----
> From: greenbuilding-bounces at listserv.repp.org
> [mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of niko
> horster
> Sent: Thursday, January 24, 2008 3:25 PM
> To: greenbuilding at listserv.repp.org
> Subject: [BULK] [Greenbuilding] controlling floor heat
> Importance: Low
>
>  
>
>  
>
> http://members.socket.net/~llile/buildgreen/Photos/radiant1.jpg
>
> http://members.socket.net/~llile/buildgreen/Photos/perimeter%20slab.jpg 
>
>  
>
> Lawrence,
>
> The photos on your site show some perimeter insulation under the slab
> and
> the section in your plans show no insulation under the slab but some on
> the
> frostwalls. I am confused as to where there actually is insulation under
> your slab. 
>
> I insulated my house slab with the now infamous bubble wrap and it is a
> little bit better than having nothing there, but not anywhere as good as
> the
> 6" of blueboard the passive house proponents place under their slabs.
> (not
> as good as the 2" under my guesthouse slab either. 
>
> It takes a while for the slab to first get going in the fall, but the
> house
> does quite well after that. I am in Vermont with a much cold clime than
> you
> in Misery (oops), but something is fishy with the performance of your
> system. What is your fuel use and what is your heat source (you
> mentioned
> tankless?) I heat mine with a Rinnai continuum commercial and work with
> a
> 20-25 degree delta across supply and return. Max usually between 108
> -120
> depending on outside temp. All but one zone are on danfoss non-electric
> thermostats with floor probes and the last zone is on airtemp sensor
> (good
> old manual thermostat and that is what shuts the pump off. One circ does
> is
> all (3600 sq or so, hard to figure as the walls are thick (Straw) and
> the
> interior partitions are masonry. So I guess the net heated space is
> probably
> around 2700-2800 sft.
>
>  
>
> niko
>
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