Ground Source Heating and Cooling Explained

Ground source heating and cooling will save you money, reduce your energy

usage and keep the environment cleaner for your family and your community.

It is the most cost-effective, energy efficient and environmentally friendly method of heating and cooling your home available today.

This information will show how you can reduce your energy bills by up to 75% today and for many years to come.

This information will answer many of your questions about how ground source systems work and how you can benefit from having a system installed.

Ground Source is able to meet all your system needs throughout New Zealand.

Ground Source Basic

How does a ground source heating and cooling system work?

Outdoor temperatures fluctuate widely with the changing seasons but underground temperatures do not.

1.2 to 2.0 meters below the earth’s surface, temperatures remain relatively constant year-round. A ground source system, which typically consists of an indoor unit and a buried earth loop, capitalizes on these constant sub-surface temperatures to provide “free” energy.

In winter (heating mode), fluid circulating through the system’s earth loop absorbs stored heat and carries it to the indoor unit. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building.

In summer (cooling mode), the system reverses, pulling heat from the building, carrying it through the earth loop and depositing it in the cooler earth.

What makes a ground source system different from ordinary systems?

Unlike ordinary systems, ground source systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth to provide a more efficient, affordable and environmentally friendly method of heating and cooling. Typically, electric power is used only to operate the unit’s fan, compressor and pump.

What are the components of a ground source system?


The three main parts consist of:

The heat-pump (indoor) unit

The liquid heat-exchange medium (open or closed loop)

The heat delivery system (such as; air-delivery ductwork or water delivery such as a hydronic floor slab).

How efficient is a ground source system?

Ground source system can be three to five times more efficient than the most efficient ordinary system.

“One of the most efficient heating and cooling systems available today” -according to The Department of Energy USA.

Ground source systems do not burn fossil fuels to make heat, they provide three to five units of energy for every one unit used to power the system.

”50 to 70% higher heating efficiencies than other heating systems”

“20 to 40% higher cooling efficiencies than available air conditioners”

US Department of Commerce and the Environmental Protection Agency


Is ground source suitable for commercial and industrial buildings?


Ground Source is very well suited to commercial and industrial applications such as hospitals, schools, offices, hotels. Infact anywhere that high heating and/or cooling loads exist.

Ground source fitted in such commercial applications operate at peak efficiency because of the ability to remove heat from areas such as kitchens or laundry areas and transfer the heat to an area requiring heating such as an office or meeting room. This allows the building remove excess heat, cooling one area and move this heat energy to area requiring heat. The same is true for cooling, at the very same time.

This is heat redistribution in the true sense of the word and is done with the absolute minimum of energy input.

This allows some commercial applications to operated at a COP’s in excess of 7.

Why do ground source systems not have a “star” rating like air-to-air heat pumps?

The existing star scale is not extensive enough to include ground source heat pumps.

Hypothetically; if the existing formula and scale were used many Waterfurnace units would exceed 12 stars on the existing 6 star scale.

Is the efficiency rating actual or just a manufacturer’s average?

All heating and cooling systems have a rated efficiency from a U.S. governmental agency.

Fossil fuel furnaces have a percentage efficiency rating. Natural gas, LPG, diesel and fuel oil furnaces have efficiency ratings based on laboratory conditions.

To get an accurate installed efficiency rating, factors such as flue gas heat losses and cycling losses caused by oversizing, blower fan electrical usage, etc., must be included.

Ground source heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance or COP.

It’s a scientific way of determining how much energy the system produces versus how much it uses. Most ground source heat pump systems have COPs of 3-5. WaterFurnace’s Envision Series have COP’s of up to 6.8. That means for every one unit of energy used to power the system, 3-5 units are supplied as heat.

Where a fossil fuel furnace may be 78-90% efficient, a ground source heat pump is about 500% efficient. Ground source heat pump manufacturers and some electric utilities use computers to accurately determine the operating efficiency of a system for your home or building.

Do ground source systems require much maintenance?

Ground source systems are practically maintenance free. When installed properly, the buried loop will last for generations. And the other half of the operation – the unit’s fan, compressor and pump – is housed indoors, protected from the harsh weather conditions. Usually, periodic checks and filter changes are the only required maintenance.

What does ground source mean for the environment?

Ground source systems work with nature, not against it, by using the solar energy naturally absorbed by the earth. They burn no fossil fuels and emit no greenhouse gases, which have been linked to global warming, acid rain and other environmental hazards.

Ground Source ™ can provide WaterFurnace earth-loop antifreeze which will not harm the environment in the unlikely event of a leak. The majority of the WaterFurnace product line uses R-410A, a performance-enhancing refrigerant that will not harm the earth’s ozone layer.

How long is the payback period for a Ground source system?

To figure this accurately, you must know how much you’ll save each year in energy costs

with a ground source system as well as the price difference between it and an ordinary heating system and central air conditioner.

As an example: If you’ll save $2000 per year with a ground source system and the price difference is $10,000, your payback will be less than five years. If you install a ground source system in a new home, the monthly savings in operating costs generally will offset the additional monthly cost in the mortgage, resulting in an immediate positive cash flow.

In a commercial application the capital payback is normally less than five years.

What is the Kilowatt size of the furnace that’s being proposed?

Ground source systems, like furnaces are designed to provide specific amounts of heat energy per hour. The term “Kilowatt (kw)” refers to how much heat can be produced by the unit in an hour.

Before you can determine what size furnace you’ll need, you must have a heat loss/heat gain calculation done on the structure. From that, an accurate determination can be made of the size of the system you’ll need.

Ground Source™ will arrange this assessment if required.

Most fossil fuel furnaces are substantially oversized for heating requirements,

resulting in increased operating cost and unpleasant temperature swings.

Ground Source Systems

Are all ground source heat pump systems alike?

No. There are different kinds of ground source heat pumps designed for specific applications.

Many ground source heat pumps, for example, are intended for use only with higher temperature ground or ground water applications.

Others will operate at entering water temperatures as low as -4°C, which are possible in closed-loop systems.

Very few brands are designed for winter heating, most ground source heat pumps will however provide summer air conditioning.

Ground source heat pumps also can differ in the way they are designed. Self-contained units combine the blower, compressor, heat exchanger and coil in a single cabinet.

How does a ground source heat pump work?

Anyone with a refrigerator or an air conditioner has witnessed the operation of a heat pump. All of these machines, rather than making heat, take existing heat and move it from a lower temperature location to a higher temperature location. Refrigerators and air conditioners are heat pumps that remove heat from colder interior spaces to warmer exterior spaces for cooling purposes. Heat pumps also move heat from a low-temperature source to a high-temperature space for heating.

An air-source heat pump, for example, extracts heat from outdoor air and pumps it indoors.

A ground source heat pump works the same way, except that its heat source is the warmth of the earth. The process of elevating low-temperature heat to over 38ºC and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion.

A refrigerant is used as the heat-transfer medium which circulates within the heat pump. The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low-temperature source (fluid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed.

The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to more than 82ºC. The hot gas then circulates through a refrigerant-to-air heat exchanger where heat is removed and pumped into the building at about 38ºC. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system’s flow is reversed.


Does a ground source system heat and cool?

Yes, ground source heat pumps so versatile is its ability to be a heating and cooling system in one. With a simple flick of a switch on your indoor thermostat, you can change from one mode to another. In the cooling mode, a ground source heat pump takes heat from indoors and transfers it to the cooler earth through either groundwater or an underground earth loop system. In the heating mode, the process is reversed.

Will the minimum entering water temperature (EWT) affect which ground source heat pump I buy?

Yes. If you have an open loop system, your entering water temperatures (EWTs) may vary widely from 20°C to 4°C.

All heat pumps can handle temperatures in the moderate-to-warm range e.g 10°C+.

Important note: A closed loop system, on the other hand, may encounter EWTs below freezing.

It’s extremely important to know what EWTs at which your heat pump will operate most efficiently.

Not all ground source heat pumps will operate efficiently these lower temperatures.

Can a ground source system also heat water?

Yes. Ground source heat pumps can provide most of your hot water needs on demand at the same high efficiencies as the heating/cooling cycles.

An option called a desuperheater can be added to most heat pumps. It will provide significant savings by heating water before it enters your hot water tank.

Should I buy a ground source system large enough to heat with no supplemental heat?

Your present energy consultant, architect or design engineer should have/be able to provide a heating and cooling load calculation (heat loss, heat gain) to guide your equipment selection.

Ground Source™ will arrange this service if required.

World wide, ground source heat pumps typically are sized to meet your cooling requirements.

Note: In New Zealand the requirement is often to design to heating load.

Depending on your heating needs, a ground source heat pump will supply 80-100 percent of your design heating load, dependant on design.

Sizing the heat pump to handle your entire heating needs may result in slightly lower heating costs, but the savings may not offset the added cost of the larger heat pump unit and larger loop installation. This should be taken into account by the system designer and economically sensible options presented.

An oversized unit may cause dehumidification problems in the cooling mode, resulting in a loss of summer comfort.

Do I need to increase the size of my electric service?

Ground source heat pumps don’t use large amounts of resistance heat so your existing service may be adequate. Generally, a 80-amp service will have enough capacity and smaller amp services may be large enough in some cases. Ground Source or your electrical contractor can determine your service needs.

Is a ground source heat pump difficult to install?

Most units are straight forward to install, particularly when they replace another forced-air system. They can be installed in areas unsuitable for fossil fuel furnaces because there is no combustion, thus no need to vent exhaust gases. Ductwork must be installed in homes that don’t have an existing air distribution system. The difficulty of installing ductwork will vary and should be assessed by a contractor.

Another popular way to use ground source technology is with in-floor radiant heating, in which hot water circulating through pipes under the floor heats the room.

Can a Ground source heat pump be added to my fossil fuel furnace?

Split systems easily can be added to existing furnaces for those wishing to have a dual-fuel heating system. Dual-fuel systems use the heat pump as the main heating source and a fossil fuel furnace as a supplement in extremely cold weather if additional heat is needed.

I have a pond nearby. Can I put a loop in it?

Yes, if it’s deep enough and large enough. A minimum of 1.8 meters in depth at its lowest level during the year is needed for a pond to be considered.

The amount of surface area required depends on the heating and cooling load of the structure.

You should opt against using water from a spring, pond, lake or river as a source for your heat pump system unless it’s proven to be free of excessive particles and organic matter. They can clog a heat pump system and make it inoperable in a short time.

I have ductwork, or existing under-floor heating. Will it work with this system?

In all probability, yes. Your installing contractor should be able to determine ductwork

requirements and any minor modifications if needed.

If your radiant under-floor system is hydronic (water) only minimal modification is required.

The Loop

Does the underground pipe system really work?

The buried pipe, or earth loop, was an important technical advancement in heat pump technology. The idea of burying pipe in the ground to gather heat energy originated in the 1940s.

New heat pump designs and more durable pipe materials have been combined to make ground source heat pumps the most efficient heating and cooling systems available.

Do I need separate ground loops for heating and cooling?

No. The same loop works for both. To switch heating to cooling, or vice versa, the flow of heat is simply reversed.

What types of loops are available?

There are two main types: open and closed.

What is an open loop system?


An open loop system uses groundwater from an ordinary well/bore as a heat source.

The groundwater is pumped into the heat pump unit where heat is extracted and the water is disposed of in an environmentally safe manner, such as reinjection back into the same aquifer or water body.

Because groundwater is a relatively constant temperature year-round, wells are an excellent heat source.

How much groundwater does an open loop system require?

The water requirement of a specific model is usually expressed in litres per minute (l.p.m.) and is listed in the unit’s specifications. Generally, the average system will use 1.6 l.p.m. per kilowatt of capacity while operating, but the amount of water required depends on the size of the unit and the manufacturer’s specifications.

Your contractor should be able to provide this information.

Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You probably will need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.

What do I do with the discharge water?

There are a number of ways to dispose of water after it has passed through the heat pump.

The open discharge method is the easiest and least expensive. Open discharge simplyinvolves releasing the water into a stream, river, lake, pond, ditch or drainage tile. Obviously, one of these alternatives must be readily available and have the capacity to accept the amount of water used by the heat pump before open discharge is feasible.

A second means of water discharge is the return well. A return well is a second well bore that returns the water to the ground aquifer. A return well must have enough capacity to dispose of the water passed through the heat pump. A new return well should be installed by a qualified well driller. Likewise, a professional should test the capacity of an existing well before it is used as a return.


Are there any laws that apply to open loop installations?

All or part of the installation may be subject to local ordinances, codes, covenants or licensing requirements. Check with local authorities to determine if any restrictions apply in your area.

Does an open loop system cause environmental damage?

No. They are pollution free. The heat pump merely removes or adds heat to the water. No pollutants are added.

The only change in the water returned to the environment is a slight increase or decrease in temperature.

Can I reclaim heat from my septic system disposal field?

No. An earth loop will reach temperatures below freezing during extreme conditions and

may freeze your septic system. Such usage is banned in many areas.

What problems can be caused by poor water quality?

Poor water quality can cause serious problems in open loop systems. Your water should be tested for hardness, acidity and iron content before a heat pump is installed. Your contractor or equipment manufacturer can tell you what level of water is acceptable. Mineral deposits can build up inside the heat pump’s heat exchanger. Sometimes a periodic cleaning with a mild acid solution is all that’s needed to remove the build-up.

Impurities, particularly iron, can eventually clog a return well. If your water has high iron content, make sure that the discharge water is not aerated before it’s injected into a return well.

What is a closed loop system?


A closed loop system uses a continuous loop of buried polyethylene pipe. The pipe is connected to the indoor heat pump to form a sealed, underground loop through which water or an environmentally friendly antifreeze-and-water solution is circulated.

A closed loop system constantly re-circulates its heat-transferring solution in pressurized pipe, unlike an open loop system that consumes water from a well.

Most closed loops are trenched horizontally in areas adjacent to the building. However, where adequate land is not available, loops are vertically bored. Any area near a home or business with appropriate soil conditions and adequate square meterage will work.

What if I don’t have room for a horizontal loop?

Closed loop systems also can be vertical. Holes are bored up to 100 metres per 6 kilowatt of heat pump capacity, depending on where you live.

U-shaped loops of pipe are inserted in the holes. The holes are then backfilled with a sealing solution.


How long will the loop pipe last?

Closed loop systems should be installed using only high-density polyethylene pipe. Properly installed, these pipes will last for many decades. They are inert to chemicals normally found in soil and have good heat conducting properties. PVC pipe should never be used.

How deep and long will my trenches be?

Trenches are normally 1.2 to 1.8 metres deep and up to 400 metres long, depending on the number of pipes in a trench. One advantage of a horizontal loop system is being able to lay the trenches according to the shape of the land.

As a rule of thumb, 7.5 to 14 meters of trench is required per kilowatt of system capacity. A well-insulated 180-square-metre home would need about a 10 kilowatt system with 75 – 140 meters of trench.

The length of the ground loop is determined by the following:

  • The peak heating (or cooling) demand of the building – this is the total kilowatts required and determines the correct selection of the WaterFurnace unit
  • The thermal conductivity of the ground – the ability of the earth to transfer heat by absorbsion and extraction at the location
  • Minimum and maximum sub-surface ground temperature – the earth temperature availiable for extraction or rejection at the location

How are the pipe sections of the loop joined?


Pipe sections are joined by thermal fusion. Thermal fusion involves heating the pipe connections and then fusing them together to form a joint that’s stronger than the original pipe.

This technique creates a secure connection to protect from leakage and contamination.

Will an earth loop affect my lawn or landscape?

No. Research has proven that loops have no adverse effect on grass, trees, or shrubs. Most horizontal loop installations use trenches about 600 milimeters wide. This, of course, will initially leave temporary bare areas, but they can easily be restored with grass seed or sod.

Vertical loops require little space and result in minimal lawn damage.

Can I install an earth loop myself?

It’s not recommended. Good earth-to-coil contact is very important for successful loop operation.

Non-professional installations may result in less-than-optimum system performance.