Manor House, Surrey

A beautiful and sustainable oak frame manor house installs a ground source heating system.

Case study summary

The customer of a beautiful sustainable oak frame manor house enlisted the help of Worcester Renewable Energy to design and install a complimentary renewable heating and hot water system.

After completing detailed heat loss calculations, Worcester Renewable Energy specified a 24kW three phase ground source heat pump, complete with 500 litre hot water cylinder and 300 litre buffer tanks accompanied by full underfloor heating throughout.

A solid floor screeded underfloor heating system was installed to the ground floor with the pipes laid closely together at 100mm centres in a spiral layout to achieve the maximum W/m2 output at the low weather compensated design flow temperatures of the system which maximises the efficiency of the heat pump and minimises running costs.

An Overlay underfloor heating system was installed on the first floor, laid on top of the intermediate floor. The system offers much higher W/m2 outputs at the low weather compensated design flow temperatures than traditional aluminium plated systems that are installed between floor joints underneath the chipboard decking acts as an insulator reducing the amount of heat transfer to the rooms above.

All the underfloor heating controls are Wifi enabled allowing the system to be controlled both locally and via the internet using smarting phones and tablets.

Mr Kennedy said “Installing a renewable energy system to compliment the sustainable ok frame the building is constructed of made perfect sense to me, especially as there is no gas available to the site.”

Customer testimonial

As the end customers, we were recommended to Worcester Renewable Energy Ltd by the appointed house builder, Border Oak. Having never embarked on the installation of a renewable energy system before, previously always having a traditional oil fired boiler, we were a little sceptical but wanted a “cleaner” alternative. 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 knowing that all the responsibility for the running of both heating and water pipes through the property was under WRE’s responsibility which meant that should any leaks arise during the installation, which they didn’t, we would have known exactly which contractor was responsible. The harmony on a site was terrific! Nothing was too much trouble to WRE’s installation manager who happily accommodated our 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 the original quote. All in all, a very professional job from a very professional company who we would highly recommend. Thank you.
Mr & Mrs Kennedy, owners.

Preliminary items

To specify the correct size of heat pump, full room by room heat loss calculations were undertaken using the U-values of the various building elements.

From the calculations the peak heating demand of the property at the external design temperature was established as well as the annual heating and hot water requirement for heating and hot water.

The thermal conductivity of the ground a metre below the surface was also obtained by excavating a number of trial pits in the area proposed for the ground loops. This, coupled with the results of the heat loss calculations enabled the size of the ground loop to be accurately calculated ensuring that 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. These were then formally communicated in a design guide for following by all parties involved resulting in works progressing smoothly and an uncompromised end solution.

Excavation

Six 55m long trenches were excavated with a width and depth of 1m, each separated from one another by 4m to allow for sufficient thermal recovery of the ground. The 4m separation 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 by 1m deep pit was also excavated to accommodate the external geothermal manifold chamber, again allowing for ease of access and working.

Trench preparation

Each trench was bedded with 100m of sand prior to the installation of the ground loops, the sand serving to both protect the ground loop pipework from any sharps in the bottom of the trenches and also to ensure good thermal contact between the ground loop pipework and surrounding ground.

Ground loop installation

The return ground loop pipework was cable tied at the head of each slinky whilst keeping it straight and against the side of the trench to maximise the amount of thermal gain.

Interconnecting pipework

Upon completion of the slinky’s ground loops, 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 is sized to ensure that the pressure drop across the brine heat exchanger, circulating pump, ground loops and header pipework itself is within the maximum permissible pressure drop at the nominal flow rater of the system.

Electrofusion welding

With all the ground loops and header pipework laid, the end of each pipe was then electrofusion welded to the appropriate connection of the geothermal manifold chamber.

This involved a strict procedure of pipe cutting, marking, scrapping, cleaning, clamping and welding to ensure dependable welds.

The end of each pipe was cut square and even using a special pipe cutter, and any burrs or shaving were removed as 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 each pipe into the fitting was also measured and the outer oxidized surface of each pipe removed to the required depth using a mechanical rotational peeling tool. The surface of each pipe then wiped with an alcohol wipe to remove any dust residue and other contaminants, a critical step to avoid any poorly welded joints.

To prevent pipe movement during the welding and cooling cycles which would adversely affect the welding process, the pipes and fittings were all clamped in place. Once these steps had all been completed the joints were then welded using an electrofusion welding machine for a specific amount of time relative to fitting being welded.

Welds were 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 the same flexibility and strength as it had prior to welding.

Ground loop pressure test

A full pressure test of the completed ground loops was carried out prior to backfilling of the trenches taking place to confirm 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 test recorded on a pressure test certificate.

Backfilling

With the installation of the ground loops 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 acting to both protect the ground loop pipework from any sharps present in the backfilling soil and also ensuring that there is good thermal contact between the ground loop pipework and backfilled substrata.

Watertight

Once the property was up to roof level and the windows were installed forming a watertight building envelope, internal works commenced. The first item being the laying of the ground floor screed containing the ground floor underfloor heating installation.

Insulation

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 then laid on top of the concreate slab prior to the screed being laid over it which contains the underfloor heating system. The insulation thereby prevents heat from the underfloor heating system travelling downwards into the concrete slab.

Ground floor underfloor heating

Rather than tacking or clipping the pipework directly to the insulation, castellation plates were installed. These ensured accurate and uniform pipe spacing as well as suspending the pipes to allow complete screed coverage around their full diameter. Because a manual screed was being used, the plates also protected the pipes from foot traffic reducing the possibility of damage whilst the screed was being laid.

Ground floor underfloor heating pipework

With the castellation plates in-situ, laying of the underfloor pipework circuits quickly progressed.

Completed ground floor underfloor heating installation

Once all the underfloor heating circuits were installed the accurate and uniform pipe spacing was evident.

First floor perimeter edging

Before the first floor underfloor heating routed gypsum fibrous boards were laid, all the rooms receiving carpet were edged with 100mm wide by 18mm thick plywood. This allowed the thin plywood overboarding to be securely fixed round the perimeter of the rooms which ensured there is no spring in the ply overboarding. The edging further ensured that no pipework is present around the perimeter of the rooms where carpet grippers were installed which could result have resulted in pipes being pieced by carpet fitters.

First floor underfloor heating

Once all the rooms requiring edging had been completed, the gypsum fibrous boards were laid and securely screwed in place to the chipboard decking beneath.  The installation of the pipework then took place into the pre-routed groves within the boards.

Underfloor heating manifolds

Once all the underfloor pipework circuits were installed the tails were connected to the underfloor heating manifolds using pre-formed bends to neatly form the 90° radius required on each pipe to transition it from a horizontal to vertical direction.

Underfloor heating pressure test

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

Completed underfloor heating manifold installations

Once completed, the underfloor heating manifolds were labelled to show which room each circuit and actuator head is serving. The energy efficient, automatically modulating circulating pump was the installed to it which modules its output dependant on the amount of underfloor heating in operation.

Commissioning

With the system fully installed the final stage of the installation was to commission it. The ground loops were flushed and filled with water and glycol to ensure they are protected down to -10°C, checked using a refractometer and the flow rates through each of the slinky’s balanced using the flow setters in the geothermal manifold chamber. The underfloor heating system was then 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. The operating parameters, such as the weather compensation heat curve and hot water temperature were then set within the ground source heat pump controller and a commissioning certificate completed with all the commissioning readings and settings recorded.

Plant room

The ground source heat pump, hot water cylinder and buffer tank have all been aligned down the right had side of the plant room allowing ease of access for operation and maintenance.

Tile floor finish

Tiles have been installed throughout the ground floor which are one of the best floor coverings for use with an underfloor heating system as they offer very little heat resistance to rising heat generated from the system pipework beneath.

Wooden floor finish

The only ground floor room not to receive a tiled floor finish was the snooker room which was installed with a herringbone wooden floor. The timber was allowed to acclimatise to the relative humidity of the room and that its moisture content checked to ensure it was less that 10% before laying as failure to allow a sufficient acclimatisation time or using timber with a water content that is too high would result in the floor warping when the underfloor heating system is in operation.

Carpet floor finish

The majority of the first floor rooms were fitted with carpet and underlay with a combined tog rating of less than 1.5 to ensure it does not act as an insulator and prevent the heat from the underfloor heating system rising into the rooms.

Completed property

The finished property which has all its heating and hot water provided by the new ground source heating system.

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