Geothermal heat transfer comes in two main types, Direct and Indirect.
Indirect uses heat from deep below the surface to heat a refrigerant, which is then used to warm up the environmental systems. The Scarborough Pool in Perth uses this type of system, providing with a constant supply of warm water to keep the pool heated and comfortable all year round.
Direct geothermal energy uses pipes that are sunk just a few metres into the ground to extract heat in winter for heating (through direct heat transfer through the metal, or via a refrigerant pumped through the pipes) and to sink the heat in summer, cooling the building.
Some buildings can utilise both systems simultaneously. NDY designed one of the first geothermal projects in Manchester. The First Street Site is a 250,000 sq m mixed use development that utilises a ground source heat pump that taps into the heat capacity of the ground, which at 12m below the surface remains fairly constant. This improves the efficiency of the building’s heating and cooling plant. Closed loop boreholes effectively use the ground as a heat “sink” throughout the year whereby energy from the ground is either rejected (cooling) or absorbed (heating) into the system.
The borehole array can then be connected to a series of water-cooled variable refrigerant flow (VRF) units, which provide both the heating and cooling for the building. This complements the other boreholes that were installed at a depth of 150m. These boreholes have the potential to provide up to 300kW of peak heat rejection, representing over 20 per cent of the cooling demand for the building. In heating mode, it has the ability to deliver 188kW of heat absorption, as well as keeping the “ramp up” costs down when heating or cooling is turned on for the day.
“These geothermal systems don’t generate electricity, but they save a lot of it in the building,” says Jeff. “Energy use in buildings accounts for about one quarter of Australia’s greenhouse emissions, and over half of this is for heating and cooling. With a geothermal system, we can slash the carbon output to basically nothing, and minimise the ongoing heating and cooling costs for the project,” he adds.
NDY has worked on several other geothermal projects around the world. Including one of the first geothermal projects in Manchester, England.
Number One First Street is a mixed use building, with tenants that include Manchester arts organisations, Cornerhouse and Library Theatre Company, a four star Melia hotel, 700 space multi storey car park, nine new restaurant/café units, student accommodation and a new public square.
The project used ground source heat pump systems to access the heat capacity of the ground, which at 12m below the surface remains fairly constant to improve the efficiency of a buildings heating and cooling plant. Closed loop boreholes effectively use the ground as an energy “sink” throughout the year whereby energy from the ground is either rejected (cooling) or absorbed (heating) into the system.
The ground source heat pump and borehole solution takes advantage of the moderate temperatures in the ground to boost the efficiency of the mechanical systems and reduce the running costs of heating and cooling plant.
The biggest advantage of such systems is gained when heating and cooling is carried out throughout the year, as the heat rejected in summer is stored in the ground and used for heating in winter.