Air Heat Pump Systems with Natural Gas Heating

[westes]

What are the best air heat pump systems that use the heat pump for cooling but use a natural gas heater for heating?

Are there any reasons to not consider that design instead of an all-electric heat pump for cooling and heating? Obviously we are hoping to save on heating costs by using cheaper natural gas, but I understand it may not be so straightforward, and in certain temperature ranges using the air heat pump for heating may be more efficient than natural gas. I guess the perfect unit would sense those conditions and switch between electric and natural gas heating based on outside conditions?

I also understand that an air heat pump does not work well with the temperature outside below 40F, so the unit would of necessity need to switch to natural gas in that case.

I would have preferred the simplicity and low operating costs of geothermal, but I have sadly concluded that this is a technology only for the extremely rich.

[HVAC_James]

There are a number of systems that do use air source heat pumps and switch automaticly to nat gas Carrier Infinity and Bryant Evolution systems

[westes]

There are a number of systems that do use air source heat pumps and switch automaticly to nat gas Carrier Infinity and Bryant Evolution systems

Do you have any experience with either of those, and how do they compare against a more standard approach of an electric condensor HVAC system combined with natural gas heater?

[beenthere]

Pretty much ALL manufacturers. Make units that can be used as dual fuel heat umps.
And you can always get straight A?C with a gas furnace.

[dandyme]

are you reffering to a kool-fire

had a ribbon burner under the o/d coil

[gary_g]

What are the best air heat pump systems that use the heat pump for cooling but use a natural gas heater for heating?

Are there any reasons to not consider that design instead of an all-electric heat pump for cooling and heating? Obviously we are hoping to save on heating costs by using cheaper natural gas, but I understand it may not be so straightforward, and in certain temperature ranges using the air heat pump for heating may be more efficient than natural gas. I guess the perfect unit would sense those conditions and switch between electric and natural gas heating based on outside conditions?

I also understand that an air heat pump does not work well with the temperature outside below 40F, so the unit would of necessity need to switch to natural gas in that case.

I would have preferred the simplicity and low operating costs of geothermal, but I have sadly concluded that this is a technology only for the extremely rich.

It sounds like you are talking about a "dual fuel" system - heat pump with gas furnace back-up. Very common.

What is your delivered price for electricity (in cents per kw-hr)? Delivered price = generation + transmission + distribution.

What is your delivered price for natural gas (in $ per therm or $ per ccf)?

Heat pumps put out heat down to below 0. They'll run contantly and the output temps/btu's drop like a rock, but they still put out heat. The question is of cost effectiveness for you, and to know that, you need to know your utility rates.

[fsprea1977]

Why not a gas-absorption heat pump? It is an air-source heat pump using natural gas instead of electricity and providing heating and cooling alternatively.
Visit ww.robur.com/us and you will find all thenecessary information

[beenthere]

An absorber would be fine. Until he finds he can only get one company in his area to work on it. Or has to wait a long time for parts when its needs a part..

[fsprea1977]

In which area is he located? Here in Europe absorption HP are pretty well known and I know that they are growing fast also in the US.

[beenthere]

In which area is he located? Here in Europe absorption HP are pretty well known and I know that they are growing fast also in the US.

How fast are they growing in the USA. And where did you hear this.

[hvacrmedic]

Do you have any experience with either of those, and how do they compare against a more standard approach of an electric condensor HVAC system combined with natural gas heater?

Net savings will require an extensive amount of calculating. Note that even if the calculations yeild $XXX.xx savings in energy dollars per year, there are no guarantees that you'll actually save anything at all in reality, it could even end up costing more in the long run. It's impossible to predict utility rate changes, maintenance costs, and equipment longevity.

In some areas dual fuel actually costs more to run, especially if the fossil fuel being used is propane. The dual fuel system also will generally cost more up front.

The primary advantage of the dual fuel system is that the furnace will operate on a portable generator, whereas the heat pump portion of the system typically will not. So with dual fuel you can heat the home during a power outage if you have, or get, a portable generator.

There are several online energy comparison calculators available. I don't have any links handy, but you can Google, or wait and somebody here might post a link or two.

I can't guarantee the accuracy of any of those calculators. Some simply do not take into account all the parameters involved, and some make assumptions that won't necessarily apply to your installation or habits.

The Infinity/Evolution systems are high end, top of the line. They provide exceptional comfort, but cost a bit more. Virtually any heat pump can be configured as dual fuel though. The options available to you, as far as equipment types, brands, and pricing can be overwhelming. If you decide on a system, the quality of the installation and set up are going to be more important than the brand. Warranties also vary considerably, so figure those into your equation.

[CynicX]

Geothermal doesnt have to be that expensive. Really depends on the type of wells required. I'm assuming in your case that is the expensive part.

Dual fuel around here is esp. cost efficient. I even went that route in my own home. Its even better around if you do have propane because propane cost are very expensive here.

Switching from gas and a/c to dual fuel is usually benefitial, switching from a heat pump to dual fuel is hit or miss. However there is usually increased comfort with a fossil fuel furnace vs heat pump air output temp.

The infinity stuff is nice because its a packaged deal. Its all designed to not only work together but work very well together. But you can use any heat pump + furnace you'll just need a good installer/tech to set it up for you...

[Tsubaki]

I read all I could before I ordered my Nordyne (Frigidaire) ihybrid 15 SEER 4 stage heat and 2 stage cool VS motor etc duel fuel package unit. We replaced an old Heil gas pack running on propane it was killing me with gas bills....... Second week in service and we have a problem with low temperature compressor startup. It will be fixed tomorrow so they say. With all these bells and whistles I can just imagine continuing problems. Technology is great WHEN IT WORKS. Really high reviews of the product but from what I understand when they changed the old E type unit to a F type that meets the Obama tax credit criteria the Nordyne engineering group had decided that a crankcase heater would be unnecessary since its 70 watts of power usage would decrease the SEER rating too much for the unit to qualify for the tax credit. They were exactly right that under normal conditions the crankcase heater is unnecessary but when the temp drops to zero for several nights and the unit has only been run on aux since the compressor lockout is setup at 30.The temp never got back above 30f for 5 days but the the sun comes out and on day 5 and shines ever so bright and warm on the poorly placed outdoor temp sensor. Then by the magic of solar energy the 9421 tstat believes it is 31f outside when in fact it is 19f, the tstat kicks the unit into heat pump mode and low and behold the copeland scroll compressor is trying to start up and hammering like it is going to knock the entire side of the house in. SLUGGING. I am negotiating for a new unit but they are going to add a heater and do a restart and test, they say the compressor is probably not harmed. How much hammering can a compressor take without damage? I may have to bring my wood stove back in from storage Sigh I thought those days were over and technology had saved me.

[beenthere]

Have them move the sensor while they are there.

need to see what the compressor sounds like after teh heat is in, and on for a day.

[Tsubaki]

Yes the sensor will be relocated I guess it was kinda a strange coincidence that this happened this way, they said the factory was already aware of the problem apparently an emergency PCA (whatever that is) had been issued to correct this problem, they are probably correct that it was not damaged since I was home and heard it when it first tried to start and cut it off after only a few seconds of the compressor slugging time. I gotta tell you when a 5 ton copeland scroll slugs it makes a noise like a shotgun going off repeatedly. I will have my ear attuned for any changes in the compressor noises. I am very pleased with the sound level of this technological miracle. The compressor wears a sound blanket and you can hardly even hear it run at all (at least before this problem developed) and the VS blower is an amazing feature you can barely hear it start and then it ramps up so slowly that it is not noticeable I like that, the old unit was an all or none proposition.

[tedkidd]

Net savings will require an extensive amount of calculating. Note that even if the calculations yeild $XXX.xx savings in energy dollars per year, there are no guarantees that you'll actually save anything at all in reality, it could even end up costing more in the long run. It's impossible to predict utility rate changes, maintenance costs, and equipment longevity.

In some areas dual fuel actually costs more to run, especially if the fossil fuel being used is propane. The dual fuel system also will generally cost more up front. MORE THAN WHAT and WHY?

The primary advantage of the dual fuel system is that the furnace will operate on a portable generator, whereas the heat pump portion of the system typically will not. So with dual fuel you can heat the home during a power outage if you have, or get, a portable generator.

If secondary advantages are:

- Additional heat stages (Infinity has 5 stages heat, 2 cooling)
- Ability to adjust the changeover temp based upon gas/electric rates (this can save BIG for propane users)
- Includes A/C - were you getting A/C? Incremental payback on NATURAL GAS is under 5 years. Propane can be as little as 1.
- Equipment runs spring and fall even if you have a cold summer (better to run your equipment once in a while, right?)
etc...

The Infinity/Evolution systems are high end, top of the line. They provide exceptional comfort, but cost a bit more. Virtually any heat pump can be configured as dual fuel though. The options available to you, as far as equipment types, brands, and pricing can be overwhelming. If you decide on a system, the quality of the installation and set up are going to be more important than the brand. Warranties also vary considerably, so figure those into your equation.

Whatever you do, many manufacturers have now followed Carrier's lead and have communicating equipment. This is the way to go. If the MFR doesn't have communicating, "NEXT!"

It would take a book to explain why - so take my word for it or spend some time searching this site on the topic.

[hvacrmedic]

If secondary advantages are:

- Additional heat stages (Infinity has 5 stages heat, 2 cooling)
- Ability to adjust the changeover temp based upon gas/electric rates (this can save BIG for propane users)
- Includes A/C - were you getting A/C? Incremental payback on NATURAL GAS is under 5 years. Propane can be as little as 1.
- Equipment runs spring and fall even if you have a cold summer (better to run your equipment once in a while, right?)
etc...




Whatever you do, many manufacturers have now followed Carrier's lead and have communicating equipment. This is the way to go. If the MFR doesn't have communicating, "NEXT!"

It would take a book to explain why - so take my word for it or spend some time searching this site on the topic.

Furnace staging can be an economical setback if the ductwork isn't located inside the conditioned space. Picture this, low stage heat, temp rise 35 deg across the furnace. Temp drop across the supply duct in the attic 20 deg. Net efficiency, less than 40%.

If you're going dual fuel strictly to save on utility bills, then don't install a multi-stage furnace unless you have first evaluated the potential for duct heat loss and have determined that it will be negligable. How many contractors know where to even begin with that? What's written on paper might be a good placebo, but it won't necessarily resemble the actuality.

FWIW, given that the hp must be shut down when switching to fossil fuel, the change in operating rates is abrupt, and can be calculated fairly well, even if not exactly. But the electric/electric hp has the advantage that even when the aux heat kicks in, the hp is still running. The change in operating cost isn't as easy to calculate, and isn't, as most people tend to automatically assume, the difference between strip heat operation and hp operation.

The COP of the electric/electric hp will still be much better than 1 even when the aux heat is engaged. In most areas, and this is just a guess, but I'd imagine that the electric/electric hp will be more cost efficient than a dual fuel system using propane as backup. In some areas it will be more cost efficient than a dual fuel system using nat gas as backup. Of course the fuel rates will heavily influence the outcome. Some of this will also depend upon the actual systems involved, and in how they are set up. If the aux heat is sized to the absolute minimum, then this will improve the efficiency of the electric/electric hp.

And don't forget about geography. In the south where the balance point is rarely ever reached, the aux heat source won't affect operting cost, because it will never be used. Conversely, in the colder regions the aux heat source may run for a large percentage of the heating season.

I urge the HO to do his/her own homework on this before deciding. HO's, get the fuel rates and other relevant information and post it here. Somebody will eventually do some rough calculations for you to help you decide what sort of system to have installed.

[tedkidd]

Furnace staging can be an economical setback if the ductwork isn't located inside the conditioned space.

NICE! Good point. BPI Mantra... "It Depends..." For my folks they're doing home performance, not just equipment, and dual fuel is a high end solution. So I forget some people leave bad situations bad.

The COP of the electric/electric hp will still be much better than 1 even when the aux heat is engaged. In most areas, and this is just a guess, but I'd imagine that the electric/electric hp will be more cost efficient than a dual fuel system using propane as backup.

Interesting. Cost effective how, Aux electric avoids defrost? Or because of propane cost?

In some areas it will be more cost efficient than a dual fuel system using nat gas as backup.

hmmm. Have to show me that. I guess if it stays warm, in which case why get dual? All about switchover at lower COP's...

And don't forget about geography. In the south where the balance point is rarely ever reached, the aux heat source won't affect operting cost, because it will never be used. Conversely, in the colder regions the aux heat source may run for a large percentage of the heating season.

I guess I was thinking up here. Didn't occur to me people bought dual fuel in Florida... So in the south dual fuel is in case... electric per kwh = gas per therm? Why do people get it down there? (Oop - the unreliable electric/backup generator thing?)

I urge the HO to do his/her own homework on this before deciding. HO's, get the fuel rates and other relevant information and post it here. Somebody will eventually do some rough calculations for you to help you decide what sort of system to have installed.

HUGE close! Definitely location dependent.
Guess I was getting a little zone 4/5 focused.
On the other hand, what electric rates are you paying...?
Wish everyone would put their locations in their profiles... Conversation changes significantly based on who/where you are holding it.