Accuracy of HSPF

yegooseMay 21, 2011

Per my other thread on GeoThermal-Math Madness, I'm still doing research on putting in GeoThermal unit.

My question today stems from a comparison I'm doing of Geo vs a Hybrid type of system. Using this xls file.. there's a section at the bottom that talks about HSPF efficiencies and how there are variances across the US.

Essentially, an 8.6 HSPF unit here in central Indiana would really only yield a 5.9 HSPF due to seasonal impacts. If that is in fact true, then my GeoThermal option looks a lot better.

So, is the xls file correct in that an 8.6 rated HSPF in central Indiana is going to be more in the 6.0 range?

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I have not studied or reviewed that excel file. I will as time is available.

If you haven't already, I hope you will take a look at this GW forum thread.


Here is a link that might be useful: Heat Pump News-13 HSPF?

    Bookmark   May 22, 2011 at 6:58PM
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So that chart is just showing what your electric backup does to your effective HPSF. It is not valid if you are considering a hybrid system.

Basically what that chart is doing is saying that in your climate you are going to use 20% electric backup so we decrease your HPSF by 20% (and throw in a 1.x factor so it might be 15% or 25%). If you backup up with NG, then the rating is invalid. I could be wrong but the fineprint says that it is valid only for electric backup.

    Bookmark   May 23, 2011 at 6:22AM
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Thanks for the info... I would have replied earlier, but for whatever reason didn't get the emails that anyone had responded.

The NG backup is not something I can use as that'll prevent me from getting the "all electric rate" from my electric company... which I really need to have to save about $500/year in reduced rates alone. Thus, the inefficiencies of an HSPF are pretty imported in my calculation (and "justification" of a GeoThermal Unit).

And I'll be doing more reading on the thread above.. thx!

    Bookmark   June 14, 2011 at 11:08PM
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Depending on where you live that defrost/backup cycle can be a big deal money wise.

Remember, geothermal has no defrost cycles - ever!

The backup only comes on when the heat loss is greater than the capacity of the HP - and then they work in tandem, COP never changes. Air-source heat pumps don't have the backup working in tandem in defrost mode - HP & backup are always working in opposition to each other in defrost mode!

Not a good thing when electrical rates are high.


    Bookmark   June 15, 2011 at 12:40AM
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Thanks fsq4cw!

I'm always glad to have your input. I posted another question last night but can seem to find it. Essentially it was in regards to the accuracy of ClimateMaster's GeoDesigner software. I get, with heat load of around 62k and cool around 35k a Geo cost of $1,100 for my 2400 sq. foot home; but also get around $1,700 when I put in my current 10 SEER 90AFUE NG equipment. But I know my costs are closer to around $1,050 for my hvac/year (including water). Thus, either the software is off or my load calcuations are too high (the calculations being done by local contractors). Reducing the load down to around 45 to 50k yields closer to what I'm seeing cost wise for my equipment and has geo around $600 total.

I've got one more guy coming out this week to take a real close look at my house and then he'll do a manual J.

I tried using this myself and actually came up with numbers in the 45k heat load range, but am not sure how accurate that calculator actually is (though it could be very accurate).

One other question, the COPs of the WaterFurnace and ClimateMasters are listed at 5.0 and 4.1 (or so). The results I'm seeing are showing the Envision (3ton) around 3.84 and ClimateMaster(4ton) at around 3.66 or so. Thus, my assumption is that I'm losing some COP due to the fact that my unit will need to run in 2nd stage part of the time... does that sound right?


    Bookmark   June 15, 2011 at 8:41AM
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