Re: OT: Anybody got a heat pump

["mark_harrison_uk2" <mph@xxxxxxxxxxxxxxx>]

--- In ukha_d@xxxxxxx, "Neil Fuller" <neil@f...> wrote:
> 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!!!).

Ahem...

The term "fluid" does NOT mean "liquid".

The term "fluid" means (and I quote) "A continuous,
amorphous
substance whose molecules move freely past one another and that has
the tendency to assume the shape of its container."

The word "fluid" means either a liquid or a gas....

Given that, as you say, it spends part of the cycle as a gas, and part
of the cycle as a liquid, I used the word "fluid" to mean, well
"fluid".

I'll concede that I was using the word "suddenly" a bit loosely
though :-)


>
> 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@a...>
> 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
> >
> >
> >
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> >
> >
> >
> >
> >