Electric Heat Pump or Gas Furnace?

[Homeowner314]

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[michael73]

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Here's all the numbers (September bills aren't here yet):
Electric - July - 2521 kWh - $231.23
Electric - August - 2500 - 2500 kWh - $232.40
Gas - July - 13.15 therms - $23.25
Gas - August - 12.18 therms - $22.47

Gas calc: ($23.25 - $22.47) / (13.15 - 12.18) = ($0.78) / (.97) = $0.80

I can't do the electric calc because as you can see my August cost was higher but kWh was lower - this is because according to my billing statement the average cost per kWh went up slightly in August.

Thoughts?

[beenthere]

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[dan sw fl]

Gas company = Vectren
City = Carmel, Indiana
Heat pump model = Bryant 264ANA (13.5 or 14 SEER and 9 HSPF)
Furnace model = Bryant 355AAV (80,000 BTU)

Full unit number for 264 ANA _ _ _ _
Cooling Coil # __________________ ___________ ___ has not been provided.

Heating Load at 2'F (~ Design Temperature) __________ " " _ " _ "
Specific cost of gas (fuel, distribution) for the winter months for each month " _ " _ " _ "
Vectren IN website is not as easy to deal with (so far) as some others in accessing the specific residential rate structure.
-------------------\

Can someone provide EXTENDED HEATING DATA in the PRODUCT SPECIFICATION (PDF file, ~30+ pages) for this BRYANT series?

I am looking for the COP Heating in the 25' to 50'F range so that the economic and heating capacity balance points
may be determined a little more accurately.
I believe COP may be slightly higher than or close to:
F _COP
25 2.6
30 2.8
35 3.0
40 3.1
45 3.2
47 3.3
50 3.4

However, using one's memory is surely not the best approach when getting down to the details.
The realistic answer to the OPs question in post #1 is always - in the details.
_

[tedkidd]

Hmmm.

Possible broken assumption here - what efficiency is being assumed on the gas side?

That efficiency has a LOT of dependencies...

[motoguy128]

Hmmm.

Possible broken assumption here - what efficiency is being assumed on the gas side?

That efficiency has a LOT of dependencies...

Does actual measured effciency in the field vary that much from the rated AFUE??? I had always figured that sicne the heat exchangers had enough mass and surface area, that effciency was fairly consistent.

[beenthere]

Does actual measured effciency in the field vary that much from the rated AFUE??? I had always figured that sicne the heat exchangers had enough mass and surface area, that effciency was fairly consistent.

On some set ups it does.

Of course, on many set ups heat pumps aren't getting their COP rating either.

[54regcab]

I think the number of heat pumps not getting their COP is higher than the number of furnaces not getting their AFUE. Low airflow (which many systems suffer from) has a bigger impact on COP than AFUE.

[tedkidd]

Choked airflow is just one commonly deficient dependency.

What about cycle time? Low fire on that furnace is likely to satisfy quicker than low stage on the pump.

How about comfort? Short cycling furnace could lead to temperature imbalance that causes crazy behaviors (thermostat fiddling, continuous fan, space heaters...), whereas long low stage output by the pump could balance the house.

[tedkidd]

Does actual measured effciency in the field vary that much from the rated AFUE??? I had always figured that sicne the heat exchangers had enough mass and surface area, that effciency was fairly consistent.

My other combustion appliance efficiency is measured more transparently, thus more effectively. It's range is 25-46 mpg. That's a pretty big swing.

Im finding you design this stuff so it gets and stays on the highway and surprising things happen to comfort and energy consumption. People who want their equipment to shut off, to NOT run, have it backwards.

The only time I want my equipment off is when there is no load.