Subject: Re: Why not use Heat Pump with solar panels?

From: Simon Webber <[email-masked]>
Date: Wed, 5 Apr 1995 10:15:40 GMT

>In article <[email-masked]>,  <[email-masked]> wrote:
>>
>>Why don't solar heating system use a regular / traditionally high tech heat
>>pump to move the heat from the solar panels to the heat storage instead of low
>>tech air, or water?
>
>  From: [email-masked] (DaveHatunen)
>
>  Let me get this straight. Instead of using a simple litle pump to use some
>  simple ol' water through simple pipes from the hot solar panel to the place

I agree with the original post. How about collecting the heat from
solar panels, piping the 'hot' water down to a heat store, then using
solar power in something like a peltier device, output the higher
temperature into the heat store (plus, of course, the solar energy
powering the device). The cooled water is then returned to the thermal
collector.

OK, so I haven't done the calculations. Peltier devices are around 50%
efficient, so you'd need 200% electrical power to heat source, but
there's no loss of energy since the electrical power is transferred
as heat into the store.

You'd end up with a higher temperature heat store, plus cool water
returned to the thermal collectors.

IMHO I might add. Anyone care to do the calculations?
Re: Why not use Heat Pump with solar panels?

---

From: [email-masked] (DaveHatunen)
Date: Thu, 6 Apr 1995 04:15:43 GMT

>  From: [email-masked] (DaveHatunen)

[...]

>  How come you gotta hide behind an anonymity service to post here? Planning to
>  throw in some dirty pictures?
>
>Now I *know* you're an idiot.  Didn't you notice the sig message before? 

[...]

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Nothing in the sig message tells me why you need to hide your identity.

-- 

    ********** DAVE HATUNEN ([email-masked]) **********
    *                Daly City California:                *
    *       where San Francisco meets The Peninsula       *
    *       and the San Andreas Fault meets the Sea       *
    *******************************************************

---

From: [email-masked] (DaveHatunen)
Date: Mon, 10 Apr 1995 22:00:15 GMT

In article <[email-masked]>,  <[email-masked]> wrote:
>  Or perhaps you're not understanding the thermodynamics involved.
>
>Perhaps...
>
>  OK. All a heat pump gains for you is the ability to store your solar heat at
>  a higher temperature. Total _solar_ heat stored will not be any greater. 
>
>Ignoring the heat lost from the solar panel to outside, yes...
>
>Ignoring the fact that without a heat pump, if the solar panel only gets up to
>80 degrees before it starts losing as much heat as it generates, and that
>without a heat pump, you're not going to be able to transfer much heat from an
>80 degree panel to an 70 degree room, yes...

That would be poor solar panel design. It's not that hard to get it
very warm, inside a panel, no matter how cloudy the day.

>Actually, I think I'm saying the same thing twice.  Basically, the heat pump
>can pump heat out of the solar panel before it would normally conduct/radiate
>out.

But so can a properly designed panel and circulating water system.

>You're right, it doesn't *add* heat (never said it did), but it *might* "save"
>heat that would be otherwise lost from the panel to the outside, by keeping the
>panel at a lower temperature.

Doubtful, due to inherent inefficiencies in the heat pump principle.

>I think what you're trying to say is that, *if* you're only getting enough
>radiation to bring the solar panel up to 80 degrees, *then* there's not enough
>heat in the panel to make it worthwhile to remove it, with a heat pump, or
>without.  If you're getting more radiation, then why not move the heat
>'naturally', instead of with a heat pump.

More or less.

>Unfortunately, you're as clear as mud!  And I don't think the problem is my
>ignorance!

It's not easy to explain. Coefficient of Performance and other stuff
has to be considered. 

>  Assume your solar collector is at y degrees, raised to that temp by the sun
>  from an ambient temp of w.
>
>  Then the hottest storage you can hope for is y degrees. But total heat (by
>  raising your storage water's temp) will be x calories. And the heat was
>  removed from the collector by water circulation lowering the collector temp
>  back to w.
>
>What this implies is that you can't heat your storage any hotter then your
>collectors.  This seems like a severe limitation to me.  Like I said, If you
>want to heat your storage water up to say 150-180 F, that means that you're
>exposing the that temperature (X) collector SF to the outside, and losing a lot
>of heat at the collector.

I don't believe any properly designed solar collection system would
have this problem in the first place.

>But you seem to feel that this is only going to be important if you're not
>collecting enough heat in marginal situations to heat the collectors hotter
>then the storage.  Well, that may be, but some of us have a *lot* of marginal
>solar days, and we need to use what we have!

And you will need a lot of "marginal" electricty from the grid to do
it.

>You are saying that I should add more storage, so that I don't need the
>(storage and collector) temperature to be so high.
>
>The other question I have, is transferring heat from the storage to the living
>space.  Isn't a low temperature storage going to make that heat transfer
>difficult as well?

Talk to people who actually do it.

>  With a heat pump you can move the same heat to the storage and cause the
>  storage water to be at a temperature higher than y. But only if you have less
>  water to raise the temperature of, so that total heat stored by raising the
>  water temp will still be x calories. That's because only x calories of solar
>  heat was available.
>
>  The part that can fool you is that the heat pump can move more heat than the
>  sun provided, by depressing the temperature of the collector below w degrees.
>  But this is _not_ solar heat. And this heat could have been put into storage
>  even if you had no solar collector at all.
>
>Well, if ambient temperature = w = 10 F, and you have a choice of heating the
>collectors to 60-80 F with a heat pump, or 100-130 F without a heat pump before
>you can begin to gain any heat, I'd obviously prefer the former!

But how much electricity will you need to do it? And remember, the
water has a large heat capacity. You will very quickly have your
collector down to -40F. 

Except heat pumps don't work very well period at temps like that. Or
people in Alaska would use them for gettin heat from the snow.

You need to calculate some real calories or BTUs in, with real temps
and real Coefficients of Performance. Throwing around stuff like the
"if you have a choice.." paragraph above isn't engineering, and what
you need is engineering. 

>
>  Obviously this is quite simplified, and I've described a batch process,
>  rather than the real-world continuous process, just so it's easier to keep
>  track of where the heat is coming from and where it is going.
>
>  Now the bad part is that it's a _lot_ cheaper to buy and run a cirulating
>  water pump than a compressor operated heat pump. And the heat pump will use
>  more electrical energy doing it. I Haven't made the calcs, but it's entirely
>  possible that you would have got more heat into storage at even a higher temp
>  if you had just put an electric heater in the storage tank and used the
>  electricity that would go to run the compressor. As far as tthe solar part
>  goes, anyway.
>
>Uh, No.  My understanding is that a heat pump can move multiple times as much
>heat as it comsumes (depending on temperature), making it much more efficient
>then simply 'burning' the energy.
>
>The question in my mind is, is the heat pump going to save more energy from
>being lost at the solar panels then it consumes.
>
>Jim.
>
>"Excuse me, did He say "Love Each Other?"
>
>"Well, actually He meant, 'try to control everyone, make them who you think they
> should be, run their lives for them, and make them miserable'."
>
>Jim Baranski                     ! Note:  I use the Anon Server to Post because
>Norwich, CT                      ! I don't have a Posting Host. So I include my
>[email-masked] ! Return Address intentionally.

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