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Saving energy

Many manufacturing plants and commercial premises pay for energy used in extracting heat from a process and pay once more for disposing of this heat. Waste heat can take the form of high temperature extract air from furnaces, extrusion machines, manufacturing plant, computers suites and lighting. Rather than let it go to waste, it can be used either to pre-heat fresh air or used to heat water for an air-conditioning system. There are also processes that use large amounts of energy to produce ice and cold water. Rather than run off the resulting cold water, this can be re-used for cooling purposes.

Italian heat pump manufacturer Clivet says that with many conventional air-conditioning systems, the heat within a given space is rejected to the atmosphere via the refrigerant based air-cooled condenser without any reclaimable energy benefits. However, this is not the case with the reverse cycle water source heat pump, which employs water as the transfer medium. Clivet's Versatemp reverse cycle heat pumps use an electrically operated reversing valve with four pipe connections to change the direction of refrigerant flow within the system so that the system is able to deliver both heating and cooling as desired.

Clivet's Andy Mayes speaking on reverse cycle heat pumps comments: "The system has an inherent energy reclaim capability that can provide both heating and cooling around a building, with terminal units either taking heat from the water loop or injecting heat into it as required.Unwanted heat is taken from areas requiring cooling and transferred via the water loop to areas requiring heating. Conversely, areas requiring heating will take heat from the water, thereby for a large percentage of the year restoring the thermal balance within the water loop."

The attraction of reverse cycle water source heat pumps is that a system can include any number of individual; self-contained units connected to the closed loop water system. This means that they can be retrofitted into older premises as well as being suitable for new builds and domestic properties. They can also have a very long working life, a fact that Clivet can point to with its Versatemp units. The Company is still coming across units fully functioning after more than 30 years' service.

The growth in demand for this type of heat pump has not been lost on other international players. Colt for one has recently introduced its Caloris system, which it says is ideal for hotels, schools, hospitals, retail premises, sport facilities and offices. Caloris systems are based on a decentralised, locally controlled arrangement of indoor heat pump units. Their design offers thermal mass energy storage and their horizontal indoor units are claimed to be amongst the quietest and slimmest in their class.

Colt Caloris systems can comprise three main units: individual indoor local heat pumps that convert the energy in water to energy in air; an external heat pump that converts the energy in air to energy in water; and a water loop to facilitate a balanced flow of water to all the local heat pumps. These systems can use both the building mass and a water reservoir (when connected to a ground source heat pump) as a heat sink for both heating and cooling purposes. It also provides additional energy efficiency and accommodates for the possible failure of an indoor unit in a series.

Using the ground as a heat source is one of the growth areas in heat pump technology, both for industrial/commercial buildings and in the domestic sector. The ground is a good energy store and has a relatively stable temperature range all year round. Collectors or probes can be set either vertically or horizontally into the ground, with the energy being delivered via a mixture of water and antifreeze (brine) to the heat pump evaporator. However, a circulating pump is required. According to manufacturers Veissmann, positive development of the heat pump market in Germany started in the 1990s and was almost exclusively for the domestic market. That said, they recognised that suitably sized heat pumps could also cover much higher output demands and in larger buildings, so-called medium sized heat pumps with an output of between 20 and 200 kW are now being used. It is worth noting that in countries such as Sweden (where sales of heat pumps exceed oil-fired boilers), medium sized heat pumps start at 100 kW output.

Mitsubishi Electric is enjoying success with its WY and WR2 ground source heat pump systems, claiming that in trials the WY has proved itself to be over 300% more efficient than a boiler/chiller combination. For the trials, the WY transfers heat from a 'slinky', a coil of plastic tubing buried horizontally in a 1.8 m deep trench, to provide the energy required to heat or coil the refrigerant circuit in the heat pump. In addition, the water sourced WY units can also transfer heat between the indoor units to further reduce energy consumption.

Mitsubishi Electric's inverter-driven WR2 units, using a vertical closed-loop bore hole system, comprising 50 holes sunk to a depth of 98 m in the ground strata have been installed at an award-winning eco-friendly building in Southend , England . With the WR2, the buildings owners, Olympus KeyMed have the facility to either cool or heat the refrigerant circuit and transfer heat between any of the 24 indoor units available on each circuit to offer double heat recovery potential and COPs (Coefficient Of Performance) of up to 7.0.

Regardless of where the heat pump extracts is source(s) of energy, it is a technology that is in the ascendancy and one that is challenging the established order of boilers and pumps for providing heating and air-conditioning. According to Veissmann, in Switzerland every third new building is equipped with an electrically operated heat pump and in Sweden 7 out of 10 new buildings rely on a heat pump.

With companies such as Mitsubishi Electric, Daiken, Clivet and Hitachi bringing out domestic systems it is a technology that is clearly gathering global momentum as governments and agencies encourage and reward the drive towards more energy efficient and eco-friendly buildings.

Contact:
Andy Mayes
Email: sales@clivet-uk.co.uk

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Previous: How does a heat pump work?

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