[Greenbuilding] Understanding Heat Pumps

[Dan Antonioli]

On Jan 10, 2008, at 6:12 PM, Keith Winston wrote:

> Hi Dan,
>
> The best way to assure a heat pump does not over-cool a space is to  
> not turn it on, in cooling mode... ;-) Seriously, the only real  
> issue is that if you don't get to count the cooling cost you're  
> saving by it's efficiency, then it's payback is going to inherently  
> be longer...
>
> COP on the Fujitsu is somewhere in the 3-4 range. But the brochure  
> I linked to earlier has peak draw, and other info in it.

I'm guessing that this means "no" to my first question. They can't be  
"heat" only.

>
> Heat pumps are most commonly installed in forced air ducted  
> systems: that is what most people think of, in fact, when you say  
> "heat pump". If you're referring to mini-splits, no they can't  
> really be incorporated, though in principle fan mode could be used  
> to move heat/coolth around. That carries an efficiency cost, since  
> fans cost money (well, electricity) to run.
>
> Cost effective? Too complicated a question. Depends on the house,  
> climate, install, even usage habits. However, SEER is linear, so if  
> you're comparing a 21 SEER Fujitsu with a 13 SEER unit, it will be  
> more than 50% more efficient, which is to say use less than 2/3 as  
> much energy. In the example I quoted before, the guy had installed  
> his own Fujitsu as the sole heating cooling unit in his small  
> house, for something like $2500. That was very cost effective!

Yes, cost effective, and energy efficient. If a device and use  
condensation to heat and cool, then that's pretty nifty, but if it  
takes a lot of energy to do it then that's part of the equation.

The example above, the Fujitsu unit for $2500, how much does it cost  
to heat and cool?

Dan


>
> Keith
>
>
>
> Dan Antonioli wrote:
>> Keith,
>>
>> As I research heat pumps and read the discussion here, there are a  
>> few issues that you might be able to clarify.
>>
>> First, in a mild climate where no air conditioning is necessary,  
>> can an air-source heat pump be employed that only functions to  
>> heat? Seems like most of the units I've seen are designed to also  
>> cool, which is redundant when you don't need cooling.
>>
>> Second, what is their efficiency or "coefficient of performance?"  
>> In other words, how many amps or watts will they draw? Remember  
>> that this discussion started with the "all electric house" theme.
>>
>> Third, can heat pumps be integrated into a forced air ducting system?
>>
>> Finally, how cost effective is this approach to whole house heating?
>>
>> Thanks in advance.
>>
>> Dan