Hanson Hall - Ground source heat pump using bore holes

Hanson Hall is a very high spec’ luxury property with a total floor area of approximately 1100 square metres. The property has all the latest technological gizmo’s and gadgets throughout, including a heating and cooling system using the latest technology and design to provide the ultimate in efficiency and performance.

The system is a large ground source heat pump installation, comprising three, modular, 3-phase, 16kW brine/water heat pumps. The ground loop, which provides the initial heat source for the heat pumps, is made up of eight, 100 metre deep, bore holes hidden in the landscaping close to the right hand side of the house. The system is designed to heat the whole house, via the under floor heating, and provide sufficient domestic hot water for the six bath/shower rooms and the pool complex. It also has the capacity to provide passive cooling of the under-floor heating system in the summer. Using the ground loop to cool the floors, instead of heating them is a very cheap way of providing good comfort levels in this luxury property during hot weather. The system can achieve a Coefficient of Performance (COP) in excess of 5:1 because the ground loop utilises deep vertical bore holes.

Drilling of the eight, 100 metres deep, bore holes begins and as can be seen, due to the somewhat messy nature of this size of drilling operation, it is a good job it is done before the garden landscaping is carried out!

In picture 3 immediately above the high density polyethylene brine loops (32mm diameter) can be seen. In this installation each loop is 100 metres long, giving a total loop length of 200 metres. An anti freeze mix of water and ethylene glycol is circulated through these pipes to extract low grade heat from the ground, which the refrigeration cycle in the heat pumps converts to higher grade, useable heat for the house. As a rough guide one 100 metre deep bore hole will provide 4 kW to 5 kW of source heat.

The property’s garage can be seen in the background of picture 2 immediately above.

The garage and adjacent landscaping shows there is no detrimental long term affect of the installation of the bore holes. The eight bore hole loops are connected to the heat pumps in the basement of the house via larger bore (90mm) high density polyethylene pipes.

         

In the basement plant room, the three brine/water heat pumps can be seen connected in parallel, via a reverse return pipe work system, which allows balanced operation and loading of the units. The silver pipe work seen above the heat pumps carries ground loop antifreeze mix (known as brine) from the bore hole pipes to the evaporative heat exchangers in the heat pumps. The pipe work is insulated to prevent condensation from forming on the incoming pipe work as the temperature of the brine coming from the ground is approximately 7 degrees Celsius in the winter and around 12 degrees in the summer. When all the heat pumps are working hard, due to the refrigeration effect of the heat pump cycle. The temperature of the brine going back to the bore holes can be well below freezing when all the heat pumps are working hard.

All three units operate to provide central heating or to heat the swimming pool. When only domestic hot water heating is required, the right hand unit operates on it’s own The modular setup of the system allows the microprocessor controllers to run the heat pumps in the most efficient and effective way, depending upon variables such as required internal temperature, pool water temperature, outside air temperature, hot water usage, etc.

In picture 1, immediately above, the grey passive cooling heat exchanger can be seen at the lower left hand end of the system. In the summer, when it is required, the controller circulates cool (approximately 12 degrees Celsius) liquid from the ground loop through one side of the heat exchanger. The water in the under floor heating system is circulated through the other side, allowing all the floors within the house to be cooled by several degrees, and the only running cost is the two circulating pumps!

In picture 2, immediately above, the heat pump buffer tank can be seen at the front right hand side of the picture. This provides a store of water for the heat pumps to heat, which can then be drawn off for either under floor heating or pool heating, depending upon requirements. The buffer tank allows the heat pumps to run more efficiently, as it is not cycling on and off. It also allows the system to achieve higher water temperatures, for the same reason.

One of the three domestic hot water storage cylinders can be seen at the right hand edge of the picture. Note the auxiliary electric immersion heater elements in the buffer cylinder and hot water cylinder to provide boost heating if required in very cold weather or in the event of a breakdown of the heat pumps. Again the controller can automatically switch these auxiliary heaters if required.

This is obviously a more complex system than the average ground source heat pump installation, however, Hanson Hall is clearly not an average domestic property.