Written by Scott Meenen N3SJH,
The ground source or Geothermal heat-pump
system is supposed to be the most energy efficient means of heating next
to solar. If you do the math it is supposed to beat natural gas.
The reason heat pumps get such a bad
reputation is that they don't deliver the heat when you need it the most,
because the outdoor coil is in the same air that is making your house cold.
If it is 10 degrees outside the coil can be below 0 or -10. With geothermal
you are dealing with ground or a body of water that is from 50 to 30. Thirty
degrees may sound cold but when it is 10 out with the wind blowing and
wind chill factors below zero then 30 is not so bad especially as far as
your system is concerned.
This Ground source system is installed
in a house in Maryland that originally had just electric forced air heating.
The electric bills were so high that the owners
did not use the electric
heat system except when they went on vacation to keep the house from
freezing. Otherwise they just burned wood or kerosene a very inexpensive
way to heat but a nuisance.
Unlike most geothermal systems this
one doesn't use vertical well or ground "slinkies". This one has the coils
buried in a body of water. This way we can cheat and use only 500 total
feet of polyethylene tubing for a 4 ton system instead of several thousand
feet. The reason for this is that water has a very good thermal conductivity
compared to dirt which is about R5 per inch.
Since this system is using a body
of water it is hoped the the temperature of the loop won't get below 40
degrees F where water is the densest. Many ground systems that are sized
too small the loop temperature can get below freezing and not thaw out
until cooling season. It turns out the water temperature runs about 30-35
when there is ice frozen on the top.
Images if heat exchanging (also known
as a chiller) portion of ground source heat pump.
Notice heat exchanging coil to right and circulating
pump and expansion tank on left.
This equipment is located in the customer's basement
near the compressor.
This geothermal system has been completely field built
except for components like the pump, heat exchanger and expansion tank.
This equipment doesn't have the refrigeration lines connected
yet. I will show that in another picture.
Purging the air from the system before
closing it up and doing a final pressurization.
On the right the author checks for proper refrigerant
flow through the sight -glass connected to the filter dryer. The 4 ton
Sporlan thermostatic expansion valve is on the left. Being a field built
system I placed the tev the best I could for installation and service.
Not shown this system like any Real refrigeration systems have a
liquid line solenoid valve. To turn this system on and off I do not stop
the compressor but instead close off the refrigerant liquid line and pump
out all the vapor from the low side and let the system go off of low pressure.
To restart the system the solenoid valve coil is energized with 24 Volts
AC. from the thermostat.
The results are in
After running this system for one month
(December 2000) the customer finally got their electric bill and the results
are staggering. This month of 2000 was one of the coldest on record for
Maryland and most of the country. Their normal electric bill in the winter
averages from $80 to $100 keeping in mind that they have used the wood
stove and kerosene heaters to keep the house warm for the last 15 years.
They have electric hot water and no clothes dryer. During this month of
December they kept the wood stove and kerosene to a minimum but did have
to run an "ice-eater" to break up ice near their piers.
The resulting electric bill was $158.00
now keep in mind that they were not using electric
heaters that would run up their bill other than the electric devices
inside the house and that the hot
water was provided by the hot gas from the compressor most of the time.
This means that their heating bill is $58 as opposed to the wood stove
and kerosene. This is a fantastic result for a 4 tons system in a rather
large home. To top it off I am having some problems with the refrigerant
heat exchanger not being adequate (the suction
pressure runs about 20psig) and I will make a new one soon.
Blower: usually a squirrel cage centrifugal air moving device. Will move
large volumes of air relatively quiet. Will use less energy with more back
Fan: a paddle type air moving device used where noise is not a major consideration.
Will use more energy with more back pressure.
Combustion blower: A blower used on high efficiency furnaces or oil burners
to move combustion air. usually 1/20 to 1/6 horsepower.
OEM: Original equipment manufacturer.
Horsepower: 746 watts
KW Kilowatt (1000 watts) or 3400 BTUs per hour
RPM: revolutions per minute.
Service factor: the extent to which a motor can be safely overloaded beyond
its name plate ratting without over heating.
Air over horsepower: The rating of a motor assuming air flow through the
windings usually as a result of the air moving device.
SAE: Society of Automotive Engineers.
Ton 12,000 BTUs per hour of heating or cooling
This page will be updated soon
Good Luck Scott
If your heat pump forms
ice outside in the heat mode click
If your air conditioner or heat pump ices
in the cooling mode click
If you have
water leaking problems with your air conditioner
click here to solve it.
For other heat pump problems click
here. For other heating system problems click
Any other questions feel free to contact us by
any of the means below. good luck Scott.
Written By: Scott
Meenen N3SJH of: G&S MECHANICAL SERVICES. Specializing in Mechanical, Controls
and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
Serving MD, DC, and Northern
VA. Contact us by pager: 1-877-467-2914