Manor House, Surrey

In order specify the correct size of heat pump, full room by room heat loss calculations were completed using the building element U-Values. From the calculations the kilowatt (KW) peak heating demand of the property at the external design temperature was establish along with the kilowatt hour (kWh) heat input requirement for heating and hot water. The thermal conductivity of the ground was also established from a geological survey report and on-site trial pit. This information coupled with the results of the heat loss calculations enabled accurate sizing of the ground loops ensuring the brine temperature entering the heat pump is always above zero degrees.

Prior to commencing work a site survey was undertaken to agree the proposed layout of the ground loops, entry points into the building and plant locations. The site survey also offers an ideal opportunity for the customer to ask site specific questions relating to the installation at an early stage. This often results in works progressing smoother and an uncompromised end solution.

Six 55m long trenches were excavated 1m wide by 1m deep. A 4m separation between trenches to allow for thermal recovery of the ground also enabled ease or working allowing plant access to drive up and down the length of the trenches and for all spoil to be piled in between. A 3m square pit was excavated to accommodate the external geothermal manifold chamber and allow for working access.

Trenches were bedded with 100m of sand prior to the installation of the ground loops. The sand serves to both protect the ground loop pipework from any sharps in the bottom of the trenches and also ensure good thermal contact between the ground loop pipework and surrounding ground.

When laying the ground loops the return pipework was cable tied at the head of each slinky keeping the pipework straight and against the side of the trench to maximise the amount of thermal gain.

Following laying of the slinky’s, the pre-insulated armoured flow and return header pipework between the geothermal manifold chamber and the plant room was laid. The diameter of the pipework had been sized to ensure that the pressure drop across the brine heat exchanger, circulating pump, ground loops and header pipework itself was within the maximum permissible pressure drop at the nominal flow rater of the system.

Once all the slinky’s and header pipework were in place the flow and return tails from each were electrofusion welded to the appropriate connections of the geothermal manifold chamber. This involved a strict procedure of pipe cutting, marking, scrapping, cleaning, clamping and welding to ensure dependable welds. The pipe ends must be cut square and even using special pipe cutters and any burrs or shaving removed. Failure to do so can leave the heating wire uncovered leading to short circuit, overheating uncontrolled melting and even sudden ignition. The insertion depth of the fitting is then measured and the outer oxidized surface of the pipe removed to the required depth using a mechanical rotational peeling tool. The prepared pipe surface is then wiped with an alcohol wipe to remove any dust residue and other contaminants. Cleaning of the prepared surface is a critical step as if not done correctly it will result in a poorly welded joint. To avoid pipe movement during the welding and cooling cycles which would adversely affect the welding process, the pipes and fitting are clamped in place. Once these steps have all been completed the joint is welded using the electrofusion welding machine for a specific amount of time relative to fitting being welded. The weld is then allowed to cool for a defined period of time to allow the unified melted pipe and fitting to cool down and solidify in a way that the material will regain its flexibility and strength as it was prior to welding. After completion of the cooling time the clamping tools are removed and the procedure repeated again for the next joint.

A full pressure test of the completed ground loops was carried out prior to backfilling taking place to ensure the absence of any leaks. The test was completed in accordance with British Standards over a predefined period of time to allow for initial expansion of the pipework. The results of the satisfactory were then recorded on a pressure test certificate.

With the ground loop installation complete and pressure tested a further 100mm of sand was laid over the top of the pipework and around the geothermal manifold chamber before backfilling with the previously excavated soil. The sand acts to both protect the ground loop pipework from any sharps present in backfilling soil and also ensures good thermal contact between the ground loop pipework and backfilled substrata.

With property up to roof level and windows installed forming a watertight envelope, internal works could commence. The first item being the laying of the ground floor screed containing the ground floor underfloor heating installation.

Unlike a traditional ground floor construction where the insulation is laid under the concrete slab, because underfloor heating was being installed a reverse slab construction was adopted. The insulation was therefore laid on top of the concreate slab prior to the screed being laid over it containing the underfloor heating system. The insulation thereby preventing heat from the underfloor heating system travelling downwards into the concrete slab.

Rather than tacking or clipping the pipework directly to the insulation, Polypipe castellation plates were installed. These ensure uniform and accurate pipe spacing as well as a complete screed coverage around the full diameter of the pipes. This is achieved as the pipes are held in a slightly suspended position in the castellation’s allowing the screed to seep under as well as over them. When laying a manual screed the plates also ensure that pipes do not get ‘kicked’ out of position from foot and wheel barrow traffic, which also reduces the possibility of damage.

With the castellation plates in-situ, laying of the underfloor pipework circuits quickly progressed. The plates allow make the laying of each circuit a one man operation meaning that two men can laid two circuits simultaneously, speeding up the installation time.

With all the circuits installed the pipe spacing and uniformity can be clearly seen.

Before the first floor underfloor heating routed boards were laid all the rooms were edged with 100mm wide x 18mm thick plywood. This ensures that when the system is overboarded secure fixings can be made around the perimeter of the rooms to ensure there is no spring in the ply overboard. The edging further ensures that no pipework is present around the perimeter of the rooms where carpet grippers are likely to be installed which could result in pipes being pieced.

With all the Polypipe gypsum fibreboards laid and securely screwed in place to the chipboard decking beneath, the installation of the pipework commenced. By using an Overlay system a much higher W/m2 output from the underfloor was achieved compared that of a traditional aluminum plated system which in contrast is installed underneath the chipboard decking between the joists. The chipboard decking then acts as an insulator preventing the heat from getting to the rooms above.

With all the underfloor pipework circuits installed the tails were then connected to the manifolds. Cold pre-formed bends were used to neatly form the 90° bends required for the pipework tails to rise vertically from the floor to the manifold ports.

Before allowing the underfloor heating systems to be screeded and ply boarded over each was pressure tested above its working pressure for any leaks. The results of the satisfactory recorded on a pressure test certificate.

The completed installation was labelled to show which room each circuit and actuator head is serving. The circulating pump installed was A rated automatically modulating its flow and power to the amount of underfloor heating that is in operation at any given time.

With the system fully installed the final stage of the installation was its commissioning. This involved each of the elements. The first being the ground loops. These were flushed and filled with water and glycol to ensure they are protected down to -10°C, checked using a refractometer. The flow rates through each of the slinky’s were then balanced using the flow setters in the geothermal manifold chamber. Secondly the underfloor heating system was filled with water and inhibited to protect it from corrosion and fungal growth. Like the ground loops the flow rates through each circuit were balanced using the flow setters on the underfloor manifolds. Finally, the operating parameters such as the weather compensation heat curve and hot water temperature were set within the ground source heat pump controller.

The main equipment has been aligned down the right had side of the plant room allowing a clear access route for operation and maintenance.

Tiles are one of the best floor coverings for use over an underfloor heating system as they offer very little heat resistance to rising heat generated from the system pipework below.

When installing a timber floor over an underfloor heating system it is imperative that the timber is first allowed to acclimatise to the relative humidity of its surroundings and that its moisture content is less that 10%. Failure to allow a sufficient acclimatisation time or using timber with a water content that is too high will result in the floor warping when the underfloor heating system is in operation.

When fitting carpets over an underfloor heating system it is imperative that the combined tog rating of the carpet and underlay is less than 1.5. If the tog value exceeds this value the carpet and underlay will act as an insulator preventing the heat form the underfloor heating system rising into the rooms.