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CF100 Questions - Page 2

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Posted by Josepi on March 14, 2010, 1:59 am
 
The heat pump doesn't stop at 1.0 COP. The COP will go much below 1.0 if
allowed to.

Usually the control circuits are set to stop the heat pump below 1.2 - 1.7
as there is no point wearing out the complex mechanism when there is usually
a backup source involved in most installations that has very few moving
parts for lot of heat.

A small heat pump in a solar thermal system could go a long way for
extracting heat. Think of the heat gain when running solution through a
solar thermal panel at +1 C. Piece of cake for heat gain.



Well, here is one way in which solar energy can help out a heat pump:

Heat pumps operate with a Coefficient of Performance (COP) of between 1.0
and
maybe 5 or 6 at the maximum.  The COP is ratio of heat produced to
electrical
energy consumed.  When COP equals 1.0, you essentially have straight
resistance
heating.  When COP is 4, then you get hot water using only 1/4 the amount of
electrical energy that simple resistance heating would require.

The main factor affecting the COP is the temperature of the source where the
heat is being pumped from.  That source can be either ambient air or water
from
a well or some other source.   For example, for my space heating I have a
geothermal heat pump using a closed loop with 2000 feet of plastic pipe
buried
in my landscaping.  When the incoming water from the loop is 50 degrees F,
then
the COP of my heat pump is about 4.0.  When the incoming water drops to 33
degrees F, as it does in late January, then the COP is down to about 1.4.
And
if the incoming temperature drops much less than that, then the heat pump
simply
stops working.

So imagine a heat pump system where low-grade solar heat (say 60 deg. F) is
used
by the heat pump to keep the COP up.  Under some conditions, such a hybrid
might
be cost-effective.

Robert Scott
Ypsilanti, Michigan



Posted by phillb on March 14, 2010, 9:19 am
 
OK
Now I am really thinking of a small heat pump water heater, after the
solar thermal water heater
For obvious use of rainy weeks, and during winter

Posted by daestrom on March 15, 2010, 11:05 pm
 Josepi wrote:

I don't think the COP of a heat pump can go below 1.0.  At 1.0, the only
heat being delivered is the energy it takes to run the compressor.

Just where could the energy to run the compressor go if not to the
condenser?  It certainly wouldn't go to the evaporator (on the suction
side of the compressor).

daestrom

Posted by Josepi on March 17, 2010, 4:29 am
 The energy to run the compressor does not need to be delivered to the
condensor or the evaporator. There are losees from the compressor and other
mechanisms, involved. The fan energy alone would be a dead loss of energy
moving air if the coil is the same temperature as the target zone.

The heat lost from the case of the compressor is not being delivered to the
desired target. A compressor could run all day, wasting energy, with it's
refrigerant valves closed. COP = 0




I don't think the COP of a heat pump can go below 1.0.  At 1.0, the only
heat being delivered is the energy it takes to run the compressor.

Just where could the energy to run the compressor go if not to the
condenser?  It certainly wouldn't go to the evaporator (on the suction
side of the compressor).

daestrom


Josepi wrote:


Posted by phillb on March 17, 2010, 9:31 pm
 So what is the possibility of using a heat pump, and having an air
tube from outside channel in, and release the cold in the basement
well, during summer that is
How about hte main idea though
What are the possible benifits of heat pump/solar hot water tank...





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