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Originally Posted by beenthere

Not sure who of them are still in business.
I think it will a waste of time because spending almost 3 hours of "googling" yesterday did not yield anything good. However, I am still in a shock after you presented me with your numbers yesterday. I just can't imagine that 3 COP HP can't do better than NG under existing energy prices. May I ask you, what sources or formulas did you use to calculate it?

2. I have a spread sheet for rough quick calcs. Doesn't allow for defrost cycles.

And I have another one set up for my areas weather. Which allows for defrost cycles. And does its calcs for the heating season, and bases the operating cost on the balance point and efficiency of the heat pump at varing weather conditions.

It is not one that I share.

I can do a more accurate calc. Not as good as I can if I have the load calc for the house, but relatively close.

Post all of what your gas and electric bills list for all charges and taxes.

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Originally Posted by energy_freak
I think it will a waste of time because spending almost 3 hours of "googling" yesterday did not yield anything good. However, I am still in a shock after you presented me with your numbers yesterday. I just can't imagine that 3 COP HP can't do better than NG under existing energy prices. May I ask you, what sources or formulas did you use to calculate it?
1 Therm = 100,000 BTU
1KW = 3414 BTU

Gas:
1,000,000 BTU = 10 Therms
95% Efficient furnace so input Therms = 10/.95 = 10.526
10.526 Therms @ \$1.25/Therm = \$13.16

HP:
1,000,000 BTU/ 3414 BTU/KW = 292.91KW
COP = 3 so input KW = 292.91/3 = 97.63KW
97.63KW @ .13/KW = \$12.69

Note that gas price is delivered gas price including all taxes, fees, etc. That is typically much higher than quoted price/Therm.

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Originally Posted by beenthere
I have a spread sheet for rough quick calcs. Doesn't allow for defrost cycles.

And I have another one set up for my areas weather. Which allows for defrost cycles. And does its calcs for the heating season, and bases the operating cost on the balance point and efficiency of the heat pump at varing weather conditions.

It is not one that I share.

I can do a more accurate calc. Not as good as I can if I have the load calc for the house, but relatively close.

Post all of what your gas and electric bills list for all charges and taxes.
The reason I did not post anything is simple. First of all our gas rates vary and swing wildly (obviously, they are highest when it is cold and /or Wall Street crooks are running those NG futures higher).

Therefore it is difficult to come up with anything meaningful. Also Nicor (our beloved utility delivering NG gas to our homes) split their billing several years ago (now they bill you for delivery / distribution and NG price component) . Obviously, what they charge for NG is directly proportional to NG futures moves and seasonal fluctuations.

In any case, based on those historical NG prices and your calculations Heat Pump option is completely out of question, at least in my case.

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Originally Posted by jkish
1 Therm = 100,000 BTU
1KW = 3414 BTU

Gas:
1,000,000 BTU = 10 Therms
95% Efficient furnace so input Therms = 10/.95 = 10.526
10.526 Therms @ \$1.25/Therm = \$13.16

HP:
1,000,000 BTU/ 3414 BTU/KW = 292.91KW
COP = 3 so input KW = 292.91/3 = 97.63KW
97.63KW @ .13/KW = \$12.69

Note that gas price is delivered gas price including all taxes, fees, etc. That is typically much higher than quoted price/Therm.
Thanks for your numbers, it's very good benchmark. Much appreciated.

6. Thats why I say post price including all taxes and transmition fee's.
Its common through out most of the country for the bill to have 4, 6 or more different charges for the gas or electric.

Whcih is why most people have a very hard time figuring out what they pay per therm delivered, or per KWH delivered.

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Originally Posted by beenthere
Thats why I say post price including all taxes and transmition fee's.
Its common through out most of the country for the bill to have 4, 6 or more different charges for the gas or electric.

Which is why most people have a very hard time figuring out what they pay per therm delivered, or per KWH delivered.
Unfortunately, in our case NG prices are changing monthly but plugging in even highest prices, it appears that running 3 COP HP is still not worth extra money you have to pay to have that option for your new system. Also, considering that there is "no intelligence" in the system controller to select proper route, those new HP systems are only feasible for those markets where NG is not available or cost prohibitive.

8. Dual fuel is not for every area.

An area with an electric rate of \$0.14(fixed) per KWH, and \$1.25(fixed) per therm for NG.
That has a heat pump with a COP of 3.5 at 47°F and a COP of 2 at 17°F outdoor temp.
Paired with a 95% efficienct furnace.
May only save \$77.00 a year.

If the gas were to go up to \$1.35(fixed), the savings would only be \$134.00 a year.
At \$1.45(fixed) it would only be \$190.00 a year.

Thats using my area's weather conditions. An a house with a 2.5 ton heat pump, with a 70 to 80,000 BTU input 95% furnace.

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## Test your comfort level in cold weather and factor that in

Originally Posted by energy_freak
Anybody knows if any of their units have the heat pump option for certain outside temperatures range (i.e. when it is 40 and above, use heat pump rather than gas)?
Are there any intelligent controllers supplied with those units which will calculate real time (based on electricity / gas unit cost) more economical route?
Since you can select the outside temperature ranges of where you want your heat pump to operate at the thermostat, you can conduct an experiment. Set the heat pump to turn off and alternate fuel on at 35 for a few days. Then do the same at 30, then at 25. You may not like the "feel" of the blower air if the HP is operating in the 25-29 range. You may not like the operation time to satisfy the setting either.

10. A Carrier engineer at the Bryant dealer meeting a couple of months ago said the new Evolution (Infinity) control will have the capability to compute the most economical heat souce, based on information gathered from the web, or manually entered by the homeowner.

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This is a great discussion and one that directly addresses the questions I've been struggling with ever since I received a quote for an Infinity hybrid system for my 2400 square foot house here in Northern Virginia. This web site was used by the salesman to help sell the hybrid system. Of course the salesman used a higher cost for NG to increase the annual savings numbers for the HP

After reading this thread, though I've come to the conclusion that unless you have a control system with direct feeds from both the gas and electric company with instantaneous energy pricing, you'll more or less be guessing when to switch from HP to NG for heating.

FWIW, I'm attaching the output from the above website. My costs are \$0.12/kWh (fixed) and \$1.50/thrm (average for Baltimore/Washington area).

12. No, that isn’t really needed with dual fuel systems, that are using a gas or oil hot air furnace for aux heat.
And are locking out the heat pump to prevent it from going into defrost.

The reason why.
Is because you base your energy savings off the temps above your heat pumps thermal balance point.
If your locking it out at 40°F to avoid having it go into defrost.

Then if you use that temps COP.
You can calculate what the lowest gas price is, that the HP will be more efficient then the gas furnace.
And then determine if your area’s gas price ever drops to or below that price.

If it doesn’t. Then there is no need to constantly change the lock out temp.

At \$0.12 per KWH for electric, at a COP of 3 for the heat pump, your natural gas price would have to drop to \$1.113 per therm, for gas to be cheaper using a 95% efficient furnace. And then, it would only be \$0.03 cheaper per 1,000,000 BTUs of delivered heat.

So how often does your gas drop below \$1.113 per therm delivered?

If you try and squeeze that last bit of savings from the heat pump. And run it at temps where it will go into defrost. You would have to allow for defrost cycles. Which would require a lot more calculations.
And the thermostat would need to know how long the defrost cycles are.

Is it really worth the extra cost of the control and programming to save \$3.00 to maybe \$12.00 a year?

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The last time it was below \$1.13/therm was in 2002. Here's a record of the prices in my area as calculated by the BLS.

If I understand your reply, it sounds like in my case a hybrid NG/HP system might have some savings.

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