Worcester Renewable Energy
Ground Source > Slinky

Manor House, Surrey

Heat Loss Calculations

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.

Site Survey

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.

Trenches Excavated

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 Sanded

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.

Ground Loops In Progress

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.

Pre-Insulated Armoured Pipework Installed

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.

Electrofusion Welding In Progress

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.

Electrofusion Welding Complete

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.

Ground Loop Installation Complete

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.

Property Watertight

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.

Ground Floor Insulation Laid

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.

Ground Floor Underfloor Heating Castellation Plates Laid

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.

Ground Floor Underfloor Heating In Progress

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.

Ground Floor Underfloor Heating Complete

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

Perimeter Edging Strips Laid

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.

First Floor Underfloor Heating Gypsum Fibreboards Laid & Installation In Progress

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.

Underfloor Heating Manifold Installation In Progress

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.

Underfloor Heating Under Pressure Test

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.

Underfloor Heating Manifold Installation Complete

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.

Ground Source Heating System Commissioning In Progress

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.

Plant Room Complete

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

Tiled Floor Installed Over Underfloor Heating System

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.

Timber Floor Installed Over Underfloor Heating System

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.

Carpets Installed Over Underfloor Heating Installation

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.

Completed Property

Project Summary

When embarking on the self-build of a beautiful sustainable oak frame manor house the customer enlisted the help of Worcester Renewable Energy to design and install a complimentary sustainable heating and hot water system. After undertaking detailed heat loss calculations a 24kW NIBE three phase ground source heat pump was specified with full underfloor heating throughout. Polypipe’s red plate solid floor screeded system was installed to the ground floor with pipes laid at 100mm centres in a spiral layout to achieve the maximum W/m2 output at the low design flow temperature of the system. The low design flow temperature maximises the efficiency of the heat pump minimising running costs. The first floor was installed with a Polypipe Overlay system on top of the intermediate floor. This offers much higher W/m2 outputs at the low design flow temperature than traditional aluminum plated systems installed between floor joints underneath the chipboard decking, which in turn, acts as an insulator reducing the amount of heat transfer to the rooms above. All controls are complete with wifi enabling the system to be controlled both locally and via the internet using smarting phones and tablets. Following completion of the installation Worcester Renewable Energy assisted the customer in making a successful application to join the Renewable Heat Incentive (RHI) scheme whereby seven years of tax free payments will be received. One of the aims of the scheme being to replay the customer for advocating the installation of a renewable technology

Key Facts

  • Heat Pump: 24kW Three Phase Ground Source Heat Pump
  • Buffer Tank: 500 Litre
  • Hot Water Storage: 500 Litre unvented cylinder with immersion backup
  • Heating Distribution: Underfloor heating
  • Hot Water Distribution: Pumped hot water return
  • Ground Loops: 6 x slinkys
  • Ground Loop Manifold: External 6 port pre-fabricated geothermal chamber
  • Interconnetion Ground Loop Pipework: Pre-insulated armoured
  • Renewable Heat Generation: 43,595kWh/year
  • CO2 Saving: 11,563kg/year

Customer Testimonial

We as a domestic end user were recommended to Worcester Renewable Energy Ltd by the appointed house builder. Having never embarked on a renewable energy source before, and previously always having a traditional oil fired boiler, we were a little skeptical but wanting a "cleaner" alternative. We thought at first the cost was too high, but after taking into account the energy saving and the Renewable Heat Incentive Scheme the numbers actually worked cost effectively. WRE’s assistance in the registration process to the RHI scheme was exceptional and went way beyond the standard level of customer service that would normally be expected. As well as all the ground source heat pump and underfloor heating, WRE's quote also included the running of hot and cold service pipes to all the bathrooms and kitchens ready for our own plumber to simply connect on to. This gave us peace of mind as all the responsibility for the running of both heating and water pipes through the building was under WRE’s responsibility which meant that should any issues/leaks arise during the installation, which they didn’t, we would of known exactly which contractor was responsible, unlike is often the case on site where there are grey areas of responsibility with one contractor blaming the other. The harmony for once on a building site was terrific! Nothing was too much trouble to WRE's site manager who happily accommodated every request and the most pleasing thing at the end of the job, apart from a terrific room by room individually controlled heating system, was that there were "no extras".... all as per quote. All in all a very professional job from a very professional company who we would highly recommend. Thank you once again for all your help and advice throughout the job. Steve & Sadie Kennedy (Property developers)