Heat pump cost calculating...

[admiralburns]

Hi folks,

I'm running a wood stove, but I'm also attempting to have a conversation with my fiance about what temperature our "default" temp should be on the thermostat when we aren't using the woodstove. I'm attempting to demonstrate the difference between keeping it at 70 degrees vs. 75 degrees. The house is 2000 sq. ft. including the basement, has fairly average insulation for a house built in 1978, an I have added blown-in insulation in the attic. I'm running a 14 SEER heat pump with forced air. I dont' need an exact number, just something approximate, and I have been researching online for 45 minutes trying to find a decent cost calculator that works, with little success. I sincerely welcome your input!

Regards,

Burns

 

[begreen]

Moved to the Green Room for a better response. Do you know the HSPF rating of your heat pump? What is your electrical rate?

 

[woodgeek]

Odds are, the difference in HP running cost 70 vs 75° might be $1-2 / day when it is below freezing out, likely <$1/day when it is above 40° outside.

Hard to be more specific without knowing the details of your install.

 

[Highbeam]

Look for a heat load or heat loss calculator. You will enter in all sorts of things about your house like SF, insulation, wall area, etc. and it will spit out a btu/hr rate that is required to maintain the specified temperature differential. You can then adjust the required temperature differential by 5 degrees and see how the btu/hr requirement changes. This change can then be calculated as a % difference, as in, it costs 10% more to heat the house to 75 than to 70.

I think it is called a Manual J calculation.

 

[Slow1]

I once went digging for a similiar answer and what I did find was an interesting stat related to programmable t-stats. The claim (and I found it in may places) was that a 1* decrease could save you 3% off your monthly heating costs. Now, clearly that doesn't directly flow in a linear fashion, but it may be closer than you think - 5* drop decreasing cost by 15%? Perhaps a close estimate. Given that we're talking heat losses here, the actualy rate of loss will be a function of the delta in indoor/outdoor temp and will be independent of source of heat. Level of insulation will reduce the rate of loss, but expressing this as a % change likely normalizes for all these things.

I'd be interested in seeing how those "Manual J calculations" that Highbeam references work out on a few scenarios and see if the % remains close to the same for a given drop in degrees in different models.

 

[jimbom]

Approximate. If the average temperature in January is 35oF and you heat to 70oF, you have to raise the indoor temperature 35oF. If you go to 75oF, then the rise is 40oF. 40/35=1.14 or 14% increase.

Average temperature of 45oF in March, then the math is 30/25=20% increase. etc

Average monthly temperatures are available on the NWS site and many others. YMMV

 

[woodgeek]

HP's cost is non-linear in BTUs at low temp. It is more than 15% if you are on the cusp of calling backup. But we don't know when the OPs system calls backup. I'd split the diff with the fiancee....run 75°F in all but the coldest 4-5 weeks of winter, and then set it down to 70.

 

[btuser]

Default temp for a fiance is whatever she wants.

Default temp for a wife is "Don't you f@#$$ng touch that thermostat!"

Seriously, after 20 years that little round dial is all that's left of my domain, and she will have to beat me to death with the remote before she prys if from my COLD dead hands.

 

[begreen]

Methinks the OP needs to find a new hot mama.

 

[btuser]

I say give her everything else, but GODDAMMIT MAN keep the thermostat!

 

[surviverguy]

Default temp for a fiance is whatever she wants.

Default temp for a wife is "Don't you f@#$$ng touch that thermostat!"

Seriously, after 20 years that little round dial is all that's left of my domain, and she will have to beat me to death with the remote before she prys if from my COLD dead hands.

Almost fell out of my chair (laughing)

 

[gtjp]

Look for a heat load or heat loss calculator. You will enter in all sorts of things about your house~~~

JP let's you know:
Hi from one who has done over 4000 studies:

www.geopros.org , 9 steps HEAT-LOSS PROVEN CORRECTING MANUAL J in 1980-1994 current to 2012
can insert diff insulation, BUT REM r-50 cellulose in an attic is like r-70 blown fiberglass, all winter long.

HEAT-LOSS calculator "click on" (behind) logo at hm pg at website: www.GEOPros.org


View attachment 63961

 

[gtjp]

Figure peak heating from not including the first 10deg you live from: we live 72, so heat loading begins at 62 to minus18 below zero::: an 80-deg design calculation. If you have 3 computers and 2 hot TV's
GUESS at air infiltration by surface area ambient exposure in sqft and mult by 1 to 3.5 for new tight with air ERV EHRV systems to loose farm house or leaky windows... X's the Surface Area exposure, block wall and all.

This load study set the current Northern States Standard leading Yoder Drilling (GEO HYDRO) and other vertical borehole drillers to realizing GT Loops needed 186 ft / compressor ton (on label in Ht Pp unit in box (not AHRI/ARI-Stickered rating )... to run 24/7 in average wet boreholes PLUS footage x's rest of LOAD/House requirement regardless of the compressor tonnage. (ie) A house load can be 7 "tons" and the unit a "4" ton::: causes consideration dor a 6-to-7 ton ground loop for great Heat Pump performance year round.

BTW: a 14 seer Air Source Ht Pp is less than half the SEER current top 6 GeoThermal Systems, properly installed. DO YOU HAVE A WELL in a wet county/ under 8% rainfall usage ? Every 3 GPM Well water at 52-54 degrees DeHumidifies and cools like a 2.1/2 ton Air Conditioner, at 6 GPM, and can water the lawn: Less than 1ppm iron, above 6.8 pH, no bacteria and hardness under 44 grains--- QUALITY and half the use of the standing water static level to production depth is ever pulled and tested in OHIO at least for 3 full days (80-hours ) .

 

[woodgeek]

The enthusiasm is a plus.....but in the OP's mild climate in VA the NPV on a geo might be poor compared to airsealing, insulating and heating the place with a mini-split.

 

[gtjp]

Inclined to agree. Even in NEOhio now with all-time low gas (5.2/mcf) and 6 cent Elect; found GT running nearly equivalent in High-Head pressure apps of low mas Radiant (106-deg and higher to even 3ft/sec runs in radiant piping) vs the only reals savings this year, in Forced-Air, 12-14% saved, any ways, or slab 80-deg fluids at 4gpm/10,000 btuh circulating GT-Hot side... closed loop at 39-deg entering in test.
GT can be adapted to existing MINI SPLIT units knowing compressor -in-box- and Hydro-Temp since the late '80's put 1.1/2 T and 2.1/2T for 3-staging together successfully to date.

Variation seems plausible only if the GT is also INSTANT HW ( please see GEOPros.com (( a begining-rough made site))) and GT Cooling is 100% heat reclaim to the HW , etc.
(4x's more then heat of just DeSuperheaters) etc- etc application driven.

In those areas referenced the load calculation sheet would be set for say 75% System of a 60-64-deg design, if enough to cool and the loop was 210 ft to (dry hole 235ft) PER COMPRESSOR (label inside box) "TON". That cooling is SEERS over 38 and COPS' of over 5+ < done in Comm offices since 1993 >
?
Applicable Direct Well cooling to a coil (hx) first stage up here where applicable, is 3 gpm / (s/Total .86) TON
and 4 gpm/ (.77 s/T) each cooling ton.

Those mini's rock, but can be 2 or three to a Hydro-Temp Staging Split, as done with Unico- heat pump coils.

 

[gtjp]

Also those Hydro-Temp Schools are under 1.8 kw / sq ft/ sch year (ALL ELECTRIC) ~ 12% more eff than secod best: ClmMstr, by ASHRAE reviews; and not 'more costly' than Trane's claim of "7% less with Ht P f/air variable".

The compact unit on stand over 30 gal HW Tank, foot print of 30"by 30" x under80" tall;
closet-through wall return; spider overhead ducting;
starting at a 3-1/2 ton ("rated's: size 4.0");
dual compressor 3-staging; 4-Zn Board IRD-Prog controller OEM built-in
with Priority Instant HW and 100% reclaimed heat (circ pumps off at the reclaim)
"...lowest 7-yr investment, maintenance and all considerations." per HUD, Arkansas re: GeoThermal Hydro-Temp Corp, AR, Systems as Earth Coupled Heat Pumps (ECL, gle).

After thorough engineer scrutinizing GT:
Gov of Tenn, to CEO:Sherwin Wms Paint Corp, Federal Reserve, and can see all Southern Schools in lists growing:

www.Hydro-Temp.com
(! Please ignore the 30-ton ditch on their hm page, as their install had dry dirt for 10-ton cooling home, before we now use horizontal drilling regularly and that pit would only be ~10x8 and a small 20-ft ditch to basement walls.) We are down to $800/ton ECL ground loop installs, plus a $ 1300 flowcenter hook up with the 1.1/8th in ID 3-way valved
FlowCenterProducts,com (near perfection- non-pressurized)
having but a reservoir-overhead-in-joists System (high NPSH in to pump) , filled-flushed , GT unit started and registered.

....