Download Final year mechanical Engg. Ground source cooling system PDF

TitleFinal year mechanical Engg. Ground source cooling system
TagsHeat Pump Hvac Air Conditioning Electromechanical Engineering
File Size564.9 KB
Total Pages21
Table of Contents
                            Engineering & Technology
	GUNUPUR – 765 022, Dist: Rayagada (Orissa), India
Document Text Contents
Page 10

solids in sand or soil. If the ground is naturally dry, soaker hoses may be buried with
the ground loop to keep it wet.

Closed loop systems need a heat exchanger between the refrigerant loop and
the water loop, and pumps in both loops. Some manufacturers have a separate ground
loop fluid pump pack, while some integrate the pumping and valving within the heat
pump. Expansion tanks and pressure relief valves may be installed on the heated fluid
side. Closed loop systems have lower efficiency than direct exchange systems, so they
require longer and larger pipe to be placed in the ground, increasing excavation costs.

Closed loop tubing can be installed horizontally as a loop field in trenches or
vertically as a series of long U-shapes in wells(see below). The size of the loop field
depends on the soil type and moisture content, the average ground temperature and
the heat loss and or gain characteristics of the building being conditioned. A rough
approximation of the initial soil temperature is the average daily temperature for the


A vertical closed loop field is composed of pipes that run vertically in the
ground. A hole is bored in the ground, typically 75 to 500 feet (23–152 m) deep. Pipe
pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole.
The borehole is commonly filled with a bentonite grout surrounding the pipe to
provide a thermal connection to the surrounding soil or rock to improve the heat
transfer. Thermally enhanced grouts are available to improve this heat transfer. Grout
also protects the ground water from contamination, and prevents artesian wells from
flooding the property. Vertical loop fields are typically used when there is a limited
area of land available. Bore holes are spaced 5–6 m apart and the depth depends on
ground and building characteristics. For illustration, a detached house needing 10 kW
(3 ton) of heating capacity might need three boreholes 80 to 110 m (270 to 350 feet)
deep.(A ton of heat is 12,000 British thermal units per hour (BTU/h) or 3.5 kilowatts.)
During the cooling season, the local temperature rise in the bore field is influenced
most by the moisture travel in the soil. Reliable heat transfer models have been
developed through sample bore holes as well as other tests.


Page 11

A 3-ton slinky loop prior to being covered with soil. The three slinky loops are
running out horizontally with three straight lines returning the end of the slinky coil to
the heat pump

A horizontal closed loop field is composed of pipes that run horizontally in the
ground. A long horizontal trench, deeper than the frost line, is dug and U-shaped or
slinky coils are placed horizontally inside the same trench. Excavation for horizontal
loop fields is about half the cost of vertical drilling, so this is the most common layout
used wherever there is adequate land available. For illustration, a detached house
needing 10 kW (3 ton) of heating capacity might need 3 loops 120 to 180 m (400 to
600 feet) long of NPS 3/4 (DN 20) or NPS 1.25 (DN 32) polyethylene tubing at a
depth of 1 to 2 m (3 to 6 feet).

As an alternative to trenching, the horizontal loop field may be laid by mini
horizontal directional drilling. (mini-HDD) This technique can lay piping under yards,
driveways or other structures without disturbing them, with a cost between those of
trenching and vertical drilling.

A slinky (also called coiled) closed loop field is a type of horizontal closed
loop where the pipes overlay each other (not a recommended method). The easiest
way of picturing a slinky field is to imagine holding a slinky on the top and bottom
with your hands and then move your hands in opposite directions. A slinky loop field
is used if there is not adequate room for a true horizontal system, but it still allows for
an easy installation. Rather than using straight pipe, slinky coils, use overlapped loops
of piping laid out horizontally along the bottom of a wide trench. Depending on soil,
climate and your heat pump's run fraction, slinky coil trenches can be anywhere from
one third to two thirds shorter than traditional horizontal loop trenches. Slinky coil
ground loops are essentially a more economic and space efficient version of a
horizontal ground loop.


12-ton pond loop system being sunk to the bottom of a pond

A closed pond loop is not common because it depends on proximity to a body
of water, where an open loop system is usually preferable. A pond loop may be
advantageous where poor water quality precludes an open loop, or where the system
heat load is small. A pond loop consists of coils of pipe - similar to a slinky loop -

Page 20

Payback period for installing a ground source heat pump in a detached

Payback period for replacing

natural gas heating oil electric heating

Canada 13 years 3 years 6 years

USA 12 years 5 years 4 years

Germany net loss 8 years 2 years


• Highly variable with energy prices.
• Government subsidies not included.

• Climate differences not evaluated.

Capital costs may be offset by substantial subsidies from many governments,
for example totaling over $7000 in Ontario for residential systems installed in the
2009 fiscal year. Some electric companies offer special rates to customers who install
a ground-source heat pump for heating/cooling their building. This is due to the fact
that electrical plants have the largest loads during summer months and much of their
capacity sits idle during winter months. This allows the electric company to use more
of their facility during the winter months and sell more electricity. It also allows them
to reduce peak usage during the summer (due to the increased efficiency of heat
pumps), thereby avoiding costly construction of new power plants. For the same
reasons, other utility companies have started to pay for the installation of ground-
source heat pumps at customer residences. They lease the systems to their customers
for a monthly fee, at a net overall savings to the customer.

The lifespan of the system is longer than conventional heating and cooling
systems. Good data on system lifespan is not yet available because the technology is
too recent, but many early systems are still operational today after 25–30 years with
routine maintenance. Most loop fields are warrantied for 25 to 50 years and are
expected to last at least 50 to 200 years. Ground-source heat pumps use electricity for
heating the house. The higher investment above conventional oil or electric systems
may be returned in energy savings in 2–10 years for residential systems in the USA.If
compared to natural gas systems, the payback period can be much longer or non-
existent. The payback period for larger commercial systems in the USA is 1–5 years,
even when compared to natural gas.

Page 21

Ground source heat pumps are recognized as one of the most efficient heating
and cooling systems on the market. They are often the second-most cost effective
solution in extreme climates, (after co-generation), despite reductions in thermal
efficiency due to ground temperature. (The ground source is warmer in climates that
need strong air conditioning, and cooler in climates that need strong heating.)

Commercial systems maintenance costs in the USA have historically been
between $0.11 to $0.22 per m2 per year in 1996 dollars, much less than the average
$0.54 per m2 per year for conventional HVAC systems.

Governments that promote renewable energy will likely offer incentives for
the consumer (residential), or industrial markets. For example, in the United States,
incentives are offered both on the state and federal levels of government.


Because of the technical knowledge and equipment needed to properly install
the piping, a GSHP system installation requires a professional's services. The
Geothermal Heat Pump Consortium and the Canadian GeoExchange Coalition
maintain listings of qualified installers in the USA and Canada.

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