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Earthtest Energy
Ground Source Heat Benefits Process Frequently Asked Questions Case Histories

Frequently Asked Questions

Cost Savings

How can savings of 85% be achieved when most companies claim up to 70% from ground source heating?

At Earthtest Energy we offer the total solution and this is tailored to the customer's requirements.

Any heat loss calculation typically shows that more than half of the heat loss from a building is caused by airflow taking heat from the building. We install whole building ventilation to ensure that the environment is healthy and odour free. We then install heat recovery, which can collect 90% of the heat from the exhausted air, and use it to warm the incoming air to within a degree or so of the prevailing internal temperature. Not all the airflow can be controlled but, dependant upon the construction and architecture of the building, about 40% of the total heat loss can be recovered.

Normally mechanical extraction and passive venting of a building takes place at high levels in a room where the temperatures are at the highest if radiator heating is used. We recommend underfloor heating, which ensures that generally the exhausted air is carrying less heat out of the building and comfort for the occupants is maximised. We install underfloor heating in a thick thermal screed to ensure its optimal performance; then subject to the preferences of the customer we install a floor surface that will enable the maximum amount of heating at the lowest water heating temperature.

The efficiency of a heat pump is directly proportional to the difference in temperature between the source heat and the heating water. By optimising the design of the underfloor heating and the choice of floor covering, water at a mean temperature of 30°C can produce a heat emission of more than 50 W/sqm with a room temperature of 21°C. By using geothermal heat from deep boreholes, we avoid the seasonal variations in ground temperature found at lesser depths. By the use of open loop systems wherever possible, we have source water entering the heat pump at 10°C to 12°C instead of 3°C or lower, which is typical for trench ground loop system.

It is this attention to detail and the management of the total solution that enables us to offer these large savings. It should be noted that the savings are dependant upon the alternative heating sources available and fuel prices prevailing; the 85% saving is on a like for like basis against electrical heating. Currently (May 2009) savings against oil and LPG would be 80% and against gas would be 75%, but tariffs vary so greatly these would need to be clarified for any particular installation.

Ventilation and Heat recovery

Can the heat recovery be switched off in summer?
Most ventilation and heat recovery systems have the facility to bring unheated air into the building, but this facility may reduce the efficiency of the heat recover. It is also possible to cool the air if this is a requirement.

Can the amount of ventilation be adjusted?
Generally ventilation systems will have three speeds of operation: Low at night, normal during the day and high when humidity or odour need to be removed. Switching between speeds can be automated if required.

What maintenance is required?
The incoming air is filtered and the filter periodically has to be changed or cleaned dependant upon the type fitted.

Is the ventilation noisy?
At low speed the ventilation is inaudible. At high speed it is significantly quieter than normal extract fans.

What are reheat batteries?
In some applications it is useful to have the air coming into the rooms in the building at a higher temperature than the exhaust air to assist in heating the building. In these cases a reheat battery is fitted to the incoming air duct after the heat recovery unit. This reheat battery can be warmed with ground source heat if required.

This is advantageous where there are restrictions which prevent the installation of underfloor heating, or where low surface temperature radiators are employed. In the latter case the incoming heated air can be used to reduce the temperature gradient through the height of the room and the extra heat enables the radiators to operate at a temperature better suited to ground source heat pumps.

Underfloor heating

Will the underfloor heating cope in very cold weather?
The system is designed to operate at a specified outside temperature. A thermostat is fitted outside the building and, in the event that the outside temperature drops, the heat pumps will increase the temperature of the water for the underfloor heating. We would normally fit a buffer tank, which would enable a significant amount of this warmer water to be stored. The warmer water passing through the underfloor heating pipes will enable the heating to cope with cold weather outside.

Can I have my bedroom cooler than my lounge?
Temperature can easily be fully controlled because the underfloor heating is installed in zones, with one or more zones per room.

Each zone is monitored by a thermostat and controlled by flow switches attached to a manifold. Each zone can be controlled with a thermostat, or a number of zones can be controlled by a single thermostat. Normally thermostats are hard wired, but wireless thermostats can be used and these can be particularly useful if changed circumstances mean that more control is required at some time in the future.

If I later decide to have thick rugs over the tiled or wood floor will the installed underfloor heat not work?
The flow rate through the underfloor heating pipes is set during commissioning, as is the temperature of the heating water. These can be adjusted to suit changes made after commissioning. Inevitably increases in the temperature of the water to compensate for the insulation of the floor by carpets would reduce the thermal efficiency of the heat pump. The laying of rugs is unlikely to reduce efficiencies significantly.

Will the water pipes leak?
The pipes we use have an infinite life and are of a four layered construction. Correctly installed they will have 100 year life.

Can I use the underfloor heating system to cool the building?
This is perfectly possible, but should ideally be specified at the onset since retrospective fitting can be problematic.

Do I need a buffer tank for my underfloor heating system?
We always specify a buffer tank, but others do not. The buffer tank reduces the on/off cycling of the heat pump, thus reducing energy wastage and reducing wear. An additional advantage is that when the weather turns very cold the temperature in the buffer tank can be increased to ensure that the building stays at its specified temperature.

Ground Source

Why do you not offer horizontal ground loops?
We always strive to achieve the most efficient heating system consistent with the customer's preferences. The warmer the source heat the greater the efficiency.

The ground above 15m varies in temperature with the seasons, since its heat is gained from the sun. The ground below 15m is at a constant and during winter and spring is at a higher temperature, since its heat is gained predominantly from the core of the earth. Therefore, Geothermal boreholes enable heat pumps to work more efficiently during the heating season.

Originally conceived trench ground loops were installed at least 2m below ground. Now health and safety considerations dictate that the trench depth is less than 1.5m and often ground conditions dictate installations at lesser depths.

Why do I need a licence to use open loop ground source?
The Environment Agency licences water extraction and water discharge to ensure that existing licensees are not adversely affected by new extraction. We can establish rapidly whether a licence will be granted and the time frame for gaining a licence should be accommodated within a construction programme.

Will drilling boreholes make a mess in my garden?
Where drilling is to be undertaken in a garden, our drillers will board the area to minimise the damage caused by the drill rig. They will use recycling tanks to catch the water and drilling materials. This photograph shows the ground loop pipes in a borehole drilled in a lawn.

Heat Pumps

How does a heat pump work?
A heat pump works by circulating a refrigerant through two heat exchangers at varying pressures. In the low pressure heat exchanger the cold liquid refrigerant absorbs latent heat from the ground source and evaporates. In the high pressure heat exchanger the hot gaseous refrigerant passes the latent heat to the heating water and condenses. The compressor, which raises the pressure in the refrigerant, uses electricity. The system is identical to that used in a refrigerator.

How can a heat pump create more heat that it uses in electricity?
A heat pump does not create heat; it moves heat up the temperature gradient making it more useful.

Is a heat pump noisy?
The heat pump is mounted in an acoustic cabinet and makes as much noise as an industrial refrigerator. It should normally be installed in a plant room or garage.

How big is a heat pump?
The heat pump for a domestic property is about the same size as a cooker. In addition, the buffer cylinder, which would normally be installed with it, is the size of a domestic hot water cylinder.

Do I need three-phase electricity?

For a domestic system single phase heat pumps are available, but for larger installations a three-phase supply is needed. All our open-loop heat pumps are available for single phase.

Is heat pump technology proven?
Yes, the technology is identical to that used in a refrigerator. Heat pumps have been used for heating for fifty years, but in the UK with the historic availability of cheap fossil fuel they only recently started to become popular.

Can a heat pump cool a building?
Yes, if it is designed to do so from the out set.


How much does it cost to install a heat pump?
We would recommend that geothermal heating is only installed as part of a complete package of measures to reduce heating costs. Typically, to install whole building ventilation with heat recovery, underfloor heating, a heat pump and boreholes would cost double or treble the cost of local extraction, radiators and a boiler.

Will I really achieve the savings in my heating bills?
Provided the design is correct, the savings will be achieved. If, however, the ventilation system is too small, the underfloor heating pipes are laid at wide spacing, the screed is too thin or the wrong specification, the ground loops are too close to the surface or the bore holes are of insufficient length, then the efficiencies can easily be lost. If heating water temperature has to be increased by 15°C to compensate for inadequacies in the ventilation or underfloor heating, the extra load results in excessive cooling of the ground and thus source heat temperatures drop by 5°C, the CoP can drop to 2.5 or below.

How can some companies offer to install systems much cheaper than others?
By reducing the efficiency of your system!

Many companies offer "whole building ventilation" which provides a managed air change every two or three hours. We recommend one air change per hour. Underfloor heating can be installed on emission plates instead of in 100mm of screed. The pitch of underfloor heating pipes can vary according to requirements or according to cost.

Inappropriate floor coverings can have a reduced life above underfloor heating and reduce its efficiency.

Trench ground loops are cheaper but less efficient than boreholes and closed loop boreholes are simpler that open loop boreholes.

Swimming Pools

Can I use a heat pump to heat my swimming pool?
A geothermal heat pump can run at peak efficiency when heating a swimming pool. SCoPs of 4 to 8 are consistently achievable. Coupled with consumption of cheap off peak electricity, the costs of heating a pool can be dramatically reduced.

Existing buildings

Can a heat pump be used with my existing radiator system?
In order for a heat pump to work efficiently, the heating water temperature needs to be lower than that normally employed in a radiator system. Typically, radiators would have to be more than doubled in heating surface to achieve the same level of heating. In applications where low surface temperature radiators are required geothermal heating can prove attractive and viable.

Can I install heat recovery, underfloor heating and heat pumps into my existing house?
The installation of heat recovery and underfloor heating is very disruptive and would normally only be tackled at the time of a major refurbishment.