Re: Re: OT: Anybody got a heat pump

["Neil Fuller" <neil@xxxxxxxxxxxxxxxxx>]

Almost correct Mark

>>As you may also remember, if you compress a fluid, it becomes
denser,
and therefore hotter.

You can't compress a fluid (ask anyone who's driven their car through a
deep
puddle and sucked in water only to find their pissed'n'broke!!!).

You actually compress warm low pressure gas which, according to Charles'
gas
law, will heat up. The heat is then removed in a condenser (this is the bit
you see hanging outside windows or, in big installations, may be a wet
cooling tower, made famous by legionnaires disease. As the heat is removed
from the high pressure gas, it condenses in to high pressure liquid. This
liquid is allowed to expand in a controlled manner (rather than suddenly!)
at which point, Charles' law and latent heat of evaporation causes the
temperature drop.

The cold gas picks up heat in the "Evaporator" (this is usually
the inside
bit of the A/C unit) over which we pass air or water to realise usable
"Coolth". As the gas moves through the evaporator, it picks up
heat (From
the air or water we are passing over it) until it is warm (as opposed to
hot) and we start the cycle again by compressing the warm gas.

With a heat pump, we basically reverse the position of the evaporator and
condenser so that the heat rejection part which is normally outside (in a
cooling system) is inside and therefore provides usable heat.

With an ordinary cooling system, the evaporator is, well, an evaporator and
the condenser is a condenser. With a heat pump, the two parts are normally
capable of changing roles so that you can "pump" your heat in to
or out of
the building.

There is a good basic explanation of the A/C cycle here
http://science.howstuffworks.com/ac1.htm

Cheers

Neil


----- Original Message -----
From: "mark_harrison_uk2" <mph@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: Monday, November 08, 2004 7:04 PM
Subject: [ukha_d] Re: OT: Anybody got a heat pump


>
>
> --- In ukha_d@xxxxxxx, "John Andrews" <groups@j...>
wrote:
>> Being ignorant - what is a heat pump?
>
>
> A device that "pumps heat", literally.
>
> As you may recall, heat can only be (net) transferred from a "hot
> thing" to a "cold thing".
>
> So, if you stick your baking disk fresh from the oven in a bowl of
> cold water, heat will transfer one way, making the disk cooler, and
> the water warmer.
>
> As you may also remember, if you compress a fluid, it becomes denser,
> and therefore hotter.
>
> A heat pump basically pumps a fluid round in a loop. The loop
> typically has two "junctions", one in a place you want to
make hotter,
> one in a place you want to make colder.
>
> When the fluid gets into the "one in a place you want to make
colder",
> it gets suddenly expanded, so it drops in temperature. Thus, all the
> heat transfers from the air around to the suddenly cold fluid. The
> fluid carries on being pumped round the loop, having been warmed en
> route, until it gets to the "place you want to make warmer",
at which
> point it is suddenly compressed, so heats up. Heat then flows OUT of
> the fluid into the surrounding areas.
>
> There are two places you use heat pumps:
>
> - Aircon / fridges, where the "place you want to make
cooler" is
> inside (the house, or the fridge), and the "place you want to
make
> warmer" is outside. In this case it's used to get over the
problem
> that, without some heat pumping, you can't transfer heat from the cold
> interior to the warm exterior.
>
> - Heaters, where the "place you want to make warmer" is
INSIDE your
> house, and the place you want to make cooler is, say, a local lake.
> (You need it to be fluid, so that the heat you are sucking out of the
> water gets spead across a huge area.)
>
> The reason you use it as a heater is that, while expensive to install,
> it is relatively efficient - typically you might get 3 times the
> amount of heat pumped in from your lake for a given amount of
> electricity as you would simply by using the electricity to power a
> heating element. The "free energy" is, obviously, coming at
the
> expense of cooling down somewhere else.
>
> Hope this helps.
>
> Regards,
>
> Mark
>
>
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> Yahoo! Groups Links
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