HVAC Unit 44 Geothermal Heat Pumps

How do heat pumps and geothermal heat pumps differ?

Geothermal heat pumps use the earth, or water in the earth, for their heat source or heat sink.

What are the two types of geothermal heat pump classifications?

1. Open-loop (or water source) systems

2. Closed loop (or earth-coupled) systems

Briefly describe an open-loop system.

It uses water from the earth such as a well, lake, or pond as the heat transfer medium and expels it back to the earth. It requires a large amount of clean water to operate properly.

Briefly describe a closed loop system.

It reuses the same heat transfer fluid that is circulated in buried plastic pipes within the earth, lake or pond.

Are defrost systems needed for geothermal heat pumps?

No, defrost systems are not needed.

What are the three water quality factors that are important for an open-loop system?

Quantity of the water available (in gpm)

Temperature of the water

Cleanliness and mineral content

Why is water cleanliness an important factor in an open-loop system

If water is contaminated, it can gradually wear down the coaxial heat exchanger. A high mineral content can foul the walls of the water side of the coaxial heat exchanger.

What do you call when water is flowing in one direction and the refrigerant is flowing in the other direction in a heat exchanger?

Counterflowing.

What is the average Delta T for the water entering and leaving an open-loop system?

The typical ranges are 7°F to 10°F.

What alloy is used for the inner tubes of heat exchangers?

Cupronickel. It has a higher corrosion resistance for acid cleaning and higher resistance to abrasion.

In a closed-loop system, what are the loops of piping called?

They are called ground loops or water loops.

What is the fluid found in a ground-loop system?

The fluid is water or a mixture of water and antifreeze.

Name the four loops in a closed-loop system

1. Water Loop or Ground Loop

2. Refrigerant Loop

3. Air Loop

4. Domestic Hot Water Loop

What does the refrigerant loop do?

It exchanges heat energy with the ground loop.

What does the air loop do?

It distributes the heated or cooled air to the building.

What does the hot water loop do?

It passes through the hot discharge line of the compressor and heats up the hot water tank.

What is the main advantage of a closed-loop system over an open-loop system?

There is no fouling of the heat exchanger since the closed-loop system uses the same treated water in the loops.

Describe the four type of ground loops

1. Vertical

2. Horizontal

3. Slinky

4. Pond/lake

What is a series flow and name a benefit using it?

A series flow only has one path for the fluid to flow along. A benefit is that it is easier to remove air that is trapped in the plastic pipe.

What is a parallel flow and name a benefit using it?

Parallel flow is similar to a electrical parallel circuit in which several parallel flow circuits of equal length connect to a supply header and a return header. A benefit of parallel is that a small diameter pipe can be used due to lower pressure drops and same money on installation.

What is the buried piping typically made of?

Polyethylene and Polybutylene

What the three types of antifreeze solutions made of?

Salts

Glycols

Alcohols

Describe a drilled well.

A well that is gets its water from an underground aquifer using a water well pump. After using the water in the open-loop system, it is discharged into a lake or stream.

Describe a return well.

They are used to discharge the water back into the ground after it has experienced the heat pump's heat exchanger. It must be spaced far apart from the supply well, typically at least 100'.

Describe a dedicated geothermal well.

This closed-loop system draws water from the top of the water column, circulates it through the heat pump and returns it at a different temperature to the bottom of the water column.

Describe a dry well.

It is used for the discharge water in an open-loop system. It is filled with gravel and sand.

What is grouting?

It is a procedure in which a cement-like material is injected between well casing and the drilled hole to prevent contamination between other water sources in the area.

What is the main purpose of a pressure tank?

To prevent short cycling of the water pump.

What is the difference between a ground loop system and a waterless earth coupled system.

Instead of using water or water/antifreeze in the ground loops, the pipes in the ground have refrigerant in them. Heat is transferred directly to or from the earth by the vaporizing refrigerant.

What are some advantages of a 'Series Flow System'?

Ease of removing trapped air

simplified flow path

Higher heat transfer per foot of pipe

What are some advantages of a 'Parallel Flow system'?

Smaller Diameter & Lower Cost Piping

Lower Installation & Labor Cost

Less Antifreeze Required

The liquid heat exchanger in a geothermal heat pump is called:

coaxial heat exchanger

water from wells or lakes is used in:

open-loop systems

water from open-loop systems may contain :

sand or clay

when there are possibilities of minerals, the heat exchanger tubes should be specified as:

cupro-nickel

when a coaxial heat exchanger becomes coated with minerals, what is used to clean it?

acid circulation

when a coaxial heat exchanger becomes coated with minerals, the COOLING cycle symptoms would be:

high head pressure

when a coaxial heat exchanger becomes coated with minerals, the HEATING cycle symptoms would be:

Low suction pressure

In a waterless , earth-coupled, closed-loop geothermal heat pump system , what is the fluid flowing in the polyethylene plastic coated copper pipes buried in the ground?

refrigerant

The waterless , earth-coupled, closed-loop geothermal heat pump system extracts heat directly from the earth and is often reffered to as a(n)_________ heat exchange with earth.

Direct

The purpose of the buffer tank on a water to water heat pump is to :

Maintain water temperature at a constant level ; Act as the water supply tank for a radiant heating system

When the water and refrigerant in a heat exchanger flow in opposite directions, it is reffered to as :

Counter flow

Many coaxial Heat exchangers are made of _____

Cupro-nickel

In a closed-loop system, the plastic water pipes that are buried in the Earth are called :

Ground loops; Water Loops

The hot gas line from the Heat pump's Compressor can be used to :

Heat Domestic Water

What is the temperature differential between water in and out of a heat exchanger that has transferred 50,000 Btu/h? The Flow Rate is 10 gallons per minute.

10 Degrees

geothermal heat pumps use the _______ or ________ as a heat source or a heat sink

Earth / Ground;Water

Geothermal heat pumps will ________heat from the earth and transfer it to the conditioned space in the winter and _______ the heat that is absorbed from the conditioned space in the summer to the earth.

transfer;move

Before deciding to purchase or install an open-loop system, the ____________ must be evaluated first

Water Quality

The ground loop configuration that is used when there is a shortage of land is the _______________.

Vertical system

__________________ heat pumps utilize two coaxial heat exchangers, as compared to only one on the water to air configuration.

Water to water

The _______________ is nothing more than a large tank that both receives water from the condenser as well as supplying water to the condenser

Buffer tank