Cathedral effect helps save energy
An innovative design and build company in Fareham, Hampshire has just released details of a highly energy efficient way of controlling the temperature within buildings using low temperature heating and high temperature cooling.
Mechanical and electrical contracting engineers, J & B Hopkins has used its headquarters in Concorde Way to demonstrate that this approach can be replicated in almost any commercial building. The company is a Business Solutions Partner with Mitsubishi Electric and offers its services across the UK.
“Concorde House was built on a brownfield site and designed around a light-weight steel frame with walls constructed from standard cladding panels,” explains Managing Director, Paul Hopkins.
Where Hopkins and his team have been truly innovative is in installing underfloor heating on both floors and also included ceiling panels with embedded pipe work to allow for cooling or heating via the ceiling.
The combination of underfloor pipe and over-ceiling systems radiates heat from both the floor and the ceiling during the heating season, or in the summer cooling season, creating an artificial thermal mass that is typically kept at between 16-19?C.
This enables the building to benefit from what Hopkins calls the ‘Cathedral Effect’ where heat from the occupants and electrical equipment is absorbed by the cooler ceiling and floor. “The heating and cooling services in the building are very adaptable in that we can run underfloor only or ceilings only in both heating and cooling or a mix of both,” comments Hopkins.
The floor systems typically need longer periods to create a constant thermal temperature as opposed to the ceilings where there is generally an instant reaction from the temperatures introduced through the pipework in both heating and cooling.
“It means that cooling can be provided at much higher temperatures or heating at lower temperatures, saving overall energy by reducing the high and low temperature requirements needed with traditional heating and cooling methods” says Hopkins.
The company is able to use a flow temperature of only 30ºC in heating mode and in cooling, the traditional need for temperatures of 10ºC or less is a thing of the past.
“We are now using temperatures for the cooling water above the dew point of 16-18ºC even mid-summer to maintain the comfort condition in the building,” he adds. “The other benefit is that we deal only with the sensible cooling element of the total cooling requirement rather than the combined latent and sensible, thereby reducing the energy requirements of the building further.”
The comfort is greater in this building even with a higher (summer) dry bulb internal air temperature. The human body temperature is around 37ºC and the heat in the body radiates to the cooler ceilings and floors. This allows the overall temperature needed for cooling to be higher than usual. The reverse is true for heating and this keeps the differentials low and helps reduce energy consumption. The overall effect is one of comfort in a steady condition.
“What we are doing is providing a suitable constant internal temperature all year round, rather than trying to always combat the fluctuating outdoor temperatures, and delivering the cooling affect through the structural absorption of the bodies radiated heat,” explains Hopkins.
The ventilation requirement for the building is also reduced because all Hopkins is asking the air services to do is deliver fresh air to people. Fully ducted heating and cooling systems typically need more air volume to carry the requisite heating and cooling loads.
Delivering only the required amount of fresh air to the occupants of the building and using a filtered heat recovery system, minimises the amount of energy needed to heat or cool the fresh air.
It also reduces the impact of ductwork in the building (less air volume therefore smaller ductwork), reduces the size of the air plant and, therefore, reduces the ventilation fan’s motor sizes and duties.
When the conditions dictate, the system also uses night-time cooling in the summer to purge the building ensuring it starts the day with a fresh and cool internal environment for the building’s total occupancy of 100 employees. Another benefit is that the building has less static because the fresh air has not had its humidity over reduced.
BSRIA (The Building Services Research and Information Association) will now be monitoring the building and systems within it, once the control systems have been linked to the underfloor heating system, and this will also give Hopkins a chance to introduce more automation into the system.
At the core of the system are two Mitsubishi Electric City Multi water sourced WR2 DX ground sourced heat pumps, two City Multi Air sourced R2 DX heat pumps and four PQFY sanitary water heating systems giving a total of around 110kw delivered active heating or cooling.
The WR2 heat pumps are fed from the slinky pipe coils buried in the car park, in a twin stack, providing around 4,000m of piping. “We have adapted the ground source system so that it uses a 50mm pipe rather than the standard 1inch pipe as we think this gives us more control over both the flow rates and temperatures,” adds Hopkins.
The geothermal slinky pipe work is able to deliver around 120kW of cooling and 100kW of heating to the building. This is being used passively during the early and late periods of the cooling season, where the cooling energy in the geothermal pipe work is extracted by using a plate heat exchanger and inverter driven pumps.
The use of both the City Multi WR2 water sourced units and the R2 air sourced units was designed to give Hopkins maximum effective control of the building’s conditions based on the outdoor air temperatures and the ground sourced water temperatures, thereby allowing the building to use the energy in its most effective and conservative means.
“We believe that a mixed usage system combining passive, active and air and ground sourced systems give us the best possible use of energy whilst delivering an effective environment,” says Hopkins.
Further use of energy within the building allows for the absorption of heat gained from the occupants, lighting, computers and printers etc. This is then circulated around the building. The underfloor and ceiling panel system provides a more balanced building so that if the sunny side is getting hotter, this heat is moved to the north side of the building to deliver building services working in equilibrium.
Concorde House also has a 60kW Broag condensing boiler able to heat to 85ºC although this has never needed to work at more than 30ºC as Hopkins explains: “We installed the boiler near to the completion of the project as at that time we hadn’t found a suitable heat pump manufacturer that could deliver heating and cooling from its plant to suit our requirements.
“During the first winter even though it was allowed to run we hardly needed it as the building has been designed to utilise energy from computers, lights, body heat, in fact wherever we can find it.”