DC heat [RE-wrenches]

[Todd Cory, Mt. Shasta Energy Services]

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It is a common misconception that heat pumps do not work well at low 
temperatures. Our air source, split (no ducts), mulit zone system still 
performs at over 200% efficiency at 10 to 15 degrees F. Our 30K btu unit 
has a 2 pole 30 breaker and "only" draws around 2500 watts running full 
out. The defrost cycle happens depending on the outside temperature and 
humidity.

I love it and it has made our home zero energy with 3.2 kWh of PV.

Todd



Geoff Greenfield wrote:

>Thanks for all the input-
>
>I could suggest heat pump to the customer, however - one of the design goals
>is simplicity (this is a remote installation in the high plateaus of Bolivia
>after all).  There is no allowance for duct work in this building, and the
>goal was to minimize battery plant, inverters and BOS... Also - my (minimal)
>understanding of Heat pumps (air source) is that at about 20 degrees they
>turn on the resistance strips anyway.... and sometimes there is a defrost
>cycle etc...  I always tell battery based folks to not try and power them
>(the last one had a 100 amp 240 breaker).  In response to Ian's thoughtful
>post I need to learn more and open my mind to such possibilities.  I am
>going to add a couple window AC units to MY house next summer....
>
>In a sense, DC resistance heating from the wind is kind of like direct water
>pumping.  In my scheme we heat the slab directly (after charging our minimal
>battery bank saved for AC loads).  Perhaps even go with two layers of heat
>and heat the deeper layer after a T-stat is satisfied.   According to David
>Katz - we can use off the shelf AC stuff with DC - this seems simple.
>(Hmmm... how about 3-phase wild AC?)  Resistance heat is inefficient, but
>also simple, reliable, easily installed and transported, avoids battery wear
>and tear and battery/inverter losses.  This is where my gut is leading me -
>any objections?
>
>For a brighter energy future,
>
>Geoff Greenfield
>NABCEP Certified Energy Practitioner
>
>THIRD SUN SOLAR & WIND POWER Ltd.
>340 West State Street
>Athens, OH 45701
>
>www.third-sun.com
>(740) 597-3111
>
>Your free subscription is suppo
>

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