A Simple Guide to Using Heat from the Ground

A ground source heat pump uses heat from the ground to help warm your home.

It works in a similar way to an air source heat pump.

However, there is one important difference.

An air source heat pump collects heat from the outside air.

A ground source heat pump collects heat from the ground.

Because ground temperatures change more slowly than air temperatures, the ground can provide a relatively stable source of heat.

The basic journey is:

Ground → Pipes → Heat pump → Heating system → Home

Let’s follow that journey.

Where Does the Heat Come From?

Even during winter, the ground contains thermal energy.

A ground source heat pump collects some of this energy through pipes buried outside the property.

Fluid flows through these pipes.

As it travels, it absorbs heat from the surrounding ground.

The warmer fluid then returns to the heat pump.

So, the first part of the journey is simple:

Ground → Buried pipes → Fluid → Heat pump

These buried pipes are often called ground loops.

Two Ways to Collect Heat

There are two common ways to install ground loops.

The first uses horizontal pipes.

The second goes much deeper underground.

Horizontal Ground Loops

If enough land is available, pipes can be buried in trenches.

These pipes spread across an area of ground and collect heat as fluid moves through them.

However, they need suitable space.

Therefore, horizontal ground loops are generally easier where a property has enough accessible land.

The amount of ground needed depends on the home, ground conditions and system design.

Boreholes

What if there is not enough land for horizontal pipes?

Another option may be to go down instead of across.

Deep holes called boreholes are drilled into the ground.

Pipework is then installed vertically.

As a result, the system can reach a large amount of ground without using the same surface area.

However, drilling boreholes is specialist work.

Therefore, this option can be more expensive.

What Happens When the Heat Reaches the Heat Pump?

The ground has now provided us with low-temperature heat.

However, that heat is not yet warm enough to heat the home effectively.

The heat pump needs to raise its temperature.

This is where the refrigerant cycle comes in.

We met the same process on the air source heat pump page.

Step 1: Collect the Heat

Fluid returns from the ground loops carrying thermal energy.

Inside the heat pump, this energy passes to a refrigerant.

The refrigerant absorbs the heat.

As a result, it can change from a liquid into a gas.

Step 2: Raise the Temperature

Next, the refrigerant gas enters the compressor.

The compressor uses electricity.

It increases the pressure of the refrigerant.

As the pressure rises, its temperature rises too.

We now have much hotter refrigerant.

Step 3: Move the Heat Into the Home

The hot refrigerant passes through another heat exchanger.

Here, its heat transfers into the water used by the home’s heating system.

That heated water can then supply:

• Radiators
• Underfloor heating
• A hot-water system

Meanwhile, the refrigerant cools.

Step 4: Start Again

Finally, the refrigerant passes through an expansion device.

Its pressure falls.

Therefore, its temperature falls too.

The refrigerant can now collect more heat.

The cycle starts again.

In simple terms:

Collect → Compress → Transfer → Expand → Repeat

That is the basic principle behind a ground source heat pump.

Why Use the Ground?

Outside air temperature can change quickly.

A mild afternoon can become a freezing night.

The ground behaves differently.

Once you move below the surface, temperature changes are generally slower.

Therefore, a ground source heat pump can draw heat from a more stable source.

This can help it perform efficiently.

However, there is a trade-off.

Getting heat from the ground requires buried pipework or boreholes.

So, installation can be much more involved than fitting an air source heat pump.

Understanding COP

Now we can introduce some simple maths.

Heat pumps use electricity.

However, electricity is not the only energy entering the system.

The heat pump is also collecting energy from the ground.

This is why it can deliver more heat energy than the electrical energy it uses.

We measure this using COP.

COP means:

Coefficient of Performance

Imagine the heat pump uses:

1 kWh of electricity

and delivers:

4 kWh of heat

The calculation is:

4 ÷ 1 = 4

So, the COP is:

4

The heat pump has not created energy from nothing.

The electricity powers the process, while much of the remaining energy comes from the ground.

COP Does Not Stay the Same

A COP of 4 does not mean the heat pump will always deliver exactly 4 kWh of heat for every 1 kWh of electricity.

Performance changes with operating conditions.

For example, the system may have to work harder when it needs to produce hotter water.

Therefore, we also use another measurement:

SCOP

This means Seasonal Coefficient of Performance.

SCOP gives a broader indication of performance across a heating season under defined conditions.

What Does SCOP Mean for Electricity Use?

Suppose a home needs:

12,000 kWh of heat

For a simple example, imagine the heat pump achieves an SCOP of:

4

We can estimate the electricity needed:

12,000 ÷ 4 = 3,000 kWh

So, in this simplified example, the heat pump would use around:

3,000 kWh of electricity

to provide:

12,000 kWh of heat

This gives us a useful calculation:

Heat needed ÷ SCOP = Approximate electricity needed

Real performance will vary.

However, the calculation helps turn SCOP into something meaningful.

Why Water Temperature Matters

The temperature of the water leaving the heat pump for your heating system is called the flow temperature.

This matters because heat pumps generally work more efficiently when they do not have to produce unnecessarily hot water.

Therefore:

Lower flow temperatures can help improve efficiency.

However, the home still needs to stay warm.

The heating system must be able to deliver enough heat to each room at those lower temperatures.

This is where radiator size and underfloor heating become important.

Can You Use Normal Radiators?

Yes.

Ground source heat pumps can work with radiators.

However, some existing radiators may be too small if they were designed for much hotter water from a boiler.

Larger radiators have more surface area.

Therefore, they can release more heat into the room at a lower water temperature.

This does not mean every radiator needs replacing.

Instead, each room should be assessed properly.

What About Underfloor Heating?

Underfloor heating can work particularly well with heat pumps.

The reason is simple.

A floor has a very large surface area.

Therefore, it can release useful amounts of heat while using relatively low water temperatures.

However, underfloor heating is not essential.

A well-designed radiator system can also work effectively.

Start With the Heat Loss

Before deciding on the heat pump, we need to understand the building.

Every home loses heat.

Heat escapes through areas such as:

• Walls
• Roof
• Windows
• Doors
• Floors
• Unwanted air leakage

A heat-loss calculation estimates how much heat the home needs to remain comfortable.

This helps determine:

• Heat-pump size
• Radiator requirements
• Flow temperatures
• Ground-loop design

Therefore, the process should really begin with:

How much heat does this home need?

Only then should we decide how to provide it.

The Ground Loop Matters Too

With a ground source system, we also need to collect enough heat from the ground.

The ground loop must therefore be designed for the property.

It cannot simply be made smaller because there is not much space available.

Ground conditions also matter.

Therefore, a proper assessment is important before deciding on the type and size of collector system.

The underground part may be invisible once installation is finished.

However, it is a vital part of the system.

What About Hot Water?

A ground source heat pump can also provide domestic hot water.

This normally involves a hot-water cylinder.

The heat pump heats the stored water, which is then available for:

• Taps
• Baths
• Showers

Hot water usually needs a higher temperature than space heating.

Therefore, hot-water requirements also need to be considered when the system is designed.

Ground Source or Air Source?

Both technologies use the same broad heat-pump principle.

The main difference is where they collect their heat.

Air Source Heat Pump

Takes heat from the outside air.

Installation is usually simpler because large-scale groundworks are not normally needed.

However, outside air temperatures can change considerably.

Ground Source Heat Pump

Takes heat from the ground.

Ground temperatures are generally more stable.

However, installation requires suitable ground loops or boreholes.

Therefore, the choice is not simply about which system is more efficient.

You also need to consider:

• Available land
• Ground conditions
• Heat demand
• Installation cost
• Disruption
• Heating system
• Property suitability

Is Ground Source Always Better?

No.

A ground source heat pump can perform very well.

However, that does not automatically make it the best option.

For example, a property may not have enough suitable land for horizontal ground loops.

Boreholes may be possible instead, but they can add considerable cost.

Meanwhile, an air source heat pump may be much easier to install.

Therefore, a slightly more efficient technology is not necessarily the better overall investment.

The better question is:

Which system suits the property?

What About Noise?

Ground source systems do not need an outdoor fan unit drawing air across a heat exchanger.

Therefore, there is no external fan operating in the same way as an air source heat pump.

However, the heat-pump unit itself still contains equipment such as:

• Compressor
• Pumps
• Controls

So, its location still deserves consideration.

Installation Is the Biggest Difference

Once installed, ground source and air source systems have many similarities.

Both:

• Use electricity
• Move heat
• Use a refrigerant cycle
• Can heat radiators
• Can work with underfloor heating
• Can provide hot water
• Use COP and SCOP to describe performance

The biggest difference is how they collect heat.

With air source:

Outside air passes through the outdoor unit.

With ground source:

Fluid collects heat through buried pipes.

That is why ground source installation can be much more involved.

In Short

A ground source heat pump collects heat from the ground and moves it into your home.

Fluid travels through buried pipes and absorbs thermal energy.

That energy reaches the heat pump.

A refrigerant then collects the heat before a compressor raises its temperature.

Finally, the heat moves into your heating and hot-water system.

The journey is:

Ground → Ground loop → Heat pump → Heating system → Home

Ground temperatures are relatively stable.

Therefore, ground source heat pumps can provide strong seasonal performance.

However, installing the ground collector can be expensive and disruptive.

So, efficiency is only part of the decision.

The property matters.

The ground matters.

The heating system matters.

And the cost matters.

A ground source heat pump can be an excellent heating system where the property and site suit the technology.

However, as with all renewable technology, the aim is not to choose the most impressive system.

It is to choose the right system for the home.

Next: How Solar Thermal Works →

Energility

Understand More. Spend Less. Live Better.