[SustainableTompkins] would solar thermal work for Ithaca?

Sat Aug 19 11:43:13 PDT 2006

See notes below.

-----Original Message-----
From: sustainabletompkins-bounces at lists.mutualaid.org
[mailto:sustainabletompkins-bounces at lists.mutualaid.org] On Behalf Of Marty
Hiller
Sent: Tuesday, August 15, 2006 11:19 PM
To: Sustainable Tompkins County listserv
Subject: Re: [SustainableTompkins] would solar thermal work for Ithaca?

Drake Landing's system uses a seasonal thermal mass to store the sun's 
heat from the warm months for use in the cold months. This pretty much 
has to be designed in when you build; you can't easily add it to an 
existing house. Here are some other examples of how it can be done:
	- I have a friend in Lincoln, MA who built a home with seasonal 
thermal mass back in the early '80's. He has an indoor swimming pool 
that collects heat all summer and gives it off all winter. He 
supplements it on cold mornings with a tiny wood stove. His one 
complaint about the system is that for most of the summer the pool is 
too cold to swim in.	- I've seen a design for an earth-sheltered house 
that uses the berm around the house as a seasonal thermal mass.
The berm is insulated from the air but thermally connected to the 
house. The insulation "umbrella" should extend about 20 feet out from 
the house, and be buried 2-3 feet deep. This is what I'd be inclined to 
try if I ever build a house. Once the thermal mass is warmed, the whole 
thing is entirely passive -- no fans, no compressors, no circulators, 
no heat exchangers, no fancy high-tech collectors: just earth.

Greg:  I am not fond of really high mass systems like this.  Too expensive
and not enough usable energy.  I like mass systems designed around daily
energy flows much more.  Much less expensive and much more responsive to the
daily swings in temperature that create our thermal comfort.  Cut your
energy needs to very low with insulation and then use mass (much less needed
because of the much lower heat loss rate) to store the peaks of solar gain
at a temperature that can heat exchange back into the house at night. Maybe
you push it up to a couple of days of storage, but that would be about it.
The lower the temperature of the storage, the more surface area required to
provide for enough heat transfer back into the space to make the system
effective.  High mass systems store heat at lower temperatures and therefore
need more surface area exposed to the inside heated space.  Both the size of
the system and the exposed area cost money, and therefore reduce cost
effectiveness. 

It's also possible to get benefits from a smaller-than-seasonal thermal 
mass. For example you might try to collect enough heat on a sunny day 
to last through a week of cloudy weather, with some other heat source 
as a backup. How much thermal mass you use determines how long you can 
go.
	- Broadmoor Nature Center in South Natick, MA 
(http://www.nesea.org/buildings/ma01.htm#boston -- scroll down for a 
description) meets 2/3 of its heating needs using an underground gravel 
pit for a thermal mass, with a south-side heat collecting room. The 
room gets very hot on sunny days, and has several large water tubes 
inside for heat collectors & additional thermal mass. They use fans to 
move the heat down into the gravel, and to circulate it through the 
building.
	- If you build slab-on-grade with radiant heat floors, you can use
the 
earth under the house as a thermal mass. That's done by creating an 
envelope of insulation that extends down into the ground around the 
perimeter of the house, while leaving the floor uninsulated, so the 
earth under the house is thermally connected to the house and is 
insulated from the earth around the house.

Greg: I strongly recommend against matching up radiant floors with high mass
underground storage.  Many of the same reasons above apply (cost
effectiveness and time frames, etc.) plus some major risks of water
intrusion stealing all your stored heat (see Marty's note below).  Plus, the
high mass system is attached to your thermal comfort system.  You end up
with a lot of unusable heat in the storage system that takes too long to get
out so the floor turns on and loses a bunch of its heat to the underfloor
storage instead of heating the house.  

I don't know the cost-benefit of any of these, but when you include the 
volatility in fuel prices you may find that it' s better than you 
expect.

You have to be careful about managing water if you use the earth for 
thermal storage (whether it's berms, earth beneath the house, or a 
borehole system like they're planning at Drake Landing). Water flowing 
underground -- or high water tables -- can siphon your heat away faster 
than anybody's business. So you have to be very sure that when it rains 
your thermal mass stays dry. That's the only gotcha I'm aware of so 
far.

- Marty

On Aug 2, 2006, at 12:51 PM, Greg Thomas wrote:

> Solar thermal works here, but mostly for domestic hot water.
>
> Solar thermal also works here as part of a well integrated building 
> system,
> typically called a "passive solar building".  By reducing the winter 
> heat
> loss, optimizing window placement and being smart with mass placement, 
> solar
> heating coming through your windows can considerably reduce your 
> already
> reduced heating load, without causing overheating.
>
> It is expensive and typically not cost effective to do more with solar
> thermal than these items in homes.  It can be done, but your money will
> usually be more effective when spent on efficiency or PV, in that 
> order.
>
> Greg Thomas
>
>
>
>
>
> -----Original Message-----
> From: sustainabletompkins-bounces at lists.mutualaid.org
> [mailto:sustainabletompkins-bounces at lists.mutualaid.org] On Behalf Of
> Patricia Haines
> Sent: Wednesday, August 02, 2006 10:11 AM
> To: Sustainable Tompkins County listserv
> Subject: [SustainableTompkins] would solar thermal work for Ithaca?
>
> Stories like that below from miles-ahead-of-us Canada are why being 
> part of
> this listserv is s
> valuable - might such an experiment - solar thermal - work here in 
> Ithaca?
>
> ----- Original Message -----
> From: GayNicholson at aol.com
> To: sustainabletompkins at lists.mutualaid.org
> Sent: Tue, 1 Aug 2006 23:59:50 EDT
> Subject: [SustainableTompkins] interesting Canadian solar community 
> under
> development
>
>> _http://dlsc.ca/index.htm_ (http://dlsc.ca/index.htm)
>>
>>
>> The Drake Landing Solar Community (DLSC) is located in Okotoks, 
>> Alberta,
> 15
>> minutes south of Calgary. The unique feature of DLSC is that  90 
>> percent
> of
>> space heating needs for the communityb
>
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-------------------------
Ours is not the task of fixing the entire world all at once, but of 
stretching out to mend the part of the world that is within our reach.
-- Clarissa Pinkola Estes

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