Trying to make sense of Geo for my large-ish scenario

Discussion in 'General Discussions' started by alx, Apr 16, 2019.

  1. alx

    alx New Member

    Hello everybody :)

    Long time lurker, but I feel my time has come to start asking questions. This forum is a gold mine for the willing.

    I am trying to make sense of Geo for my home situation which is as follows:

    I have a fairly large (7000+ sq feet) contemporary house. My Manual J is around 110k btu on both heating and cooling side. I also have an indoor pool. House is heated (very comfortably) with oil. I have two oil boilers - one 75k btu serving 6 zones (5 heating and an indirect hot water heater), the other 85k btu boiler serving 3 zones (two heating and the indirect pool heater). All heating zones are hydronic baseboard, but I have modified them also for hydronic air (inserted heat exchangers in the central ac ducts) wired as a second stage heat. Lets ignore the AC side for the moment ( I have central AC with 4x 4 ton outdoor condensers- I used the ducting to insert my heat exchangers for the 2nd stage heat as mentioned). All hydronic loops are driven by Taco ECM smart pumps running on 20 degrees delta T. This works really really well.

    My feel is that due to the complex nature of my heating system and the fact that it is dialed in it would be best if I just replace the boilers as the source of hot water. I run very well tuned (over couple years) outdoor reset on both boilers and my design day (0 degrees for my area) is satisfied with 170 degree water at the max volume of 20 gal/ minute. There are gshp that almost give me that. So I should be able to realize some savings and enjoy the green impact I make on the environment- right?

    ... But it just doesnt make ($$$$) sense to me. I will explain.

    I know that companies like Nordic have hydronic GSHP capable of 160 degree water (Maritime WC80H or even the smaller ones) and almost 100k btu. I can _almost_ make this work if I overdrive my 2nd stage heat (matter of programming which I can handle) on design day. But... looking at the install manual for that heat pump it shows 2.3 COP and almost 11kw consumption. At 0.25 cents per kw of electricity (I know- expensive) this pump will use almost 13 kw of electricity which equals to $3.00 to produce 100k btu... all the while oil at 80% efficiency will get that for $2.50 (one gallon) at current prices.

    What am I missing? I really like geo and the whole idea behind it and I despise oil, but...

    Any ideas? Random thoughts?

    Thank you
    Last edited: Apr 16, 2019

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