What's the formula?

Timco

The unit's 'rating tag' is for max fuse, or breaker. It only gets close to that on start-up. Use a amp-probe and take a running readig of each phase, or conductor one at a time to to get a better idea of what the unit is pulling.

Tim

Craig Bergman

KWH how to?

I am trying to figure out how many KWH a customers twin water to water Ground Source Heat Pumps are costing them.
Their electric bill last month was $800.00 and I need to prove to them that the Geo is not to blame.

I placed an hour meter on the low voltage side of each unit, to track the total run times. Unit 1 has 236V at 15 Amps. Unit 2 has 236V at 16 Amps. So....

236X15=3540 Watts (3.540 KW) 236X16=3776 Watts (3.776KW)
Correct so far?

3.540 KW X 1 Hr = 3.540 KWH...Correct?
3.54KWH X 7 cents= .2478 or .25 cents per hour to run this unit. Is my math all messed up or am I no the right track?

Thanks
Bergy

Craig Bergman

Those are..

the numbers of the units when running.
236V @ 15 Amps and 236 V @ 16 Amps

Bergy

Constantin

so, you're running about 7 kW when the units are running. That's 49 cents per hour at 7 cents per kW. Multiply that by 24 hours and you get up to $12 per day. Multiply that by 30 days and you get up to $360 per month. Halfway there assuming the units are running 100% of the time. If the units can modulate, the draw could even be higher during colder periods.

I would measure the actual kW draw of the heating system as a whole when the units are running. You may find that the balance of plant, i.e. the zone circulators, etc. will add significant loads as well. Simply turn off the rest of the house, crank up the heat and clock the kW meter.

However, the biggest thing to check in my mind is whether the emergency strip/resistance heaters (if fitted) come on at all and if the controls are properly wired. If emergency heat is fitted, I'd disconnect and see what happens.

ChasMan

To answer the question though, yes it is correct.. But 7 cents per KWH is the cost of electricity, dont forget distribution and taxes and surcharges etc...

Geo_7

kwh

That sound cheap,I think it .15 cents Per KWH around Boston?.

ChasMan

Yes, What I do is take my bill, 116.32 and divide it by what they say I used 772 kwh and I get .156, thats in Conecticut.

Constantin

Depends also what Utility you're with...

... some utilities give steep discounts to those heating with electric "heat".

However, comparing the theoretical kWh recorded vs. the kWh that the Geo system can pull in a month may be a good start. That eliminates the whole question of rates, etc.

S Ebels

You back from India?

Or are you chiming in from there?

Got any pics?

mark smith

$800 ... and Geo ..

what ...?? yer gonna blame the Refrigerator and TV..??

Constantin

Yeah, I'm back...

... and I have lots pf pics, some even relevant for the hydronic side of the Wall. :-)

Currently though I am girding for battle with the local fire prevention bureau over our sprinkler installation, details to follow. In essence, the Deputy Chief is interpreting the code differently than I do, making requirements that I believe the code neither requires nor intends. The time has come to beat the drums of war...

Plumdog_2

there is a reason for everything

I wondered out loud why the marketing materials touted huge gas savings but never mentioned anything about electricity. Kept almost secret in fact.

Rich W

Pump & Dump?

If it is a pump&dump don't forget the pump draw. Also look for a leaking water valve if it is. Around here we've been running into colder water this year for some reason- around 40 to 44deg. inlet temp.BRRR

Terry

happened to me

In my oldplace, I started getting ridiculous electric bills.

I took a look at me metre & it was running like mad.

one by one - I started shutting off breakers and once I got to the Refrigerator. The Wheels alsmost came to a stop.

I pulled the Fridgeout & found the floor burned badly.
It appears that the Fridge Motor was running freelance and it burned up alot of KWH's.

Makes me wonder if their making a Fridge with DC motors yet?

EIN

Tom_35

There's more to it---

than just the formulas mentioned. Power factor also has to be figured in, but that is really a minor thing.

The bigger issue is the actual btu being delivered by the heat pump. You are getting the KW that was consumed by the heat pump when you follow the formula, but what you don't know is did the heat pump, or air conditioner, or whatever, actually produce the capacity that it was supposed to for the KW consumed?

I compressor can not be pumping to it's rated capacity, the system can have air or moisture in the refrigerant circuit, etc and the unit ends up at less than expected performance.

There are formulas to find the true efficiency of the system, which is really the only way of discovering a given efficiency.

National Comfort Institue has produced heating and cooling formulas that provide "real" system efficiencies. They call them CSER for cooling and HSER for heating.

Tom Atchley