Daikin scales up its Altherma air-source heat-pump concept
Ahead of decarbonising the UK’s electricity supply and Government financial incentives, Daikin has enlarged the scope of Altherma air-source heat pumps
Heat pumps to provide space heating and domestic hot water in buildings are an accepted method of reducing carbon emissions — and will become even more so in the future as the electricity supply in the UK is decarbonised. Technically it matters little whether the decarbonised electricity comes from nuclear power stations or renewable energy; that is the stuff of politics.
In the UK, heat pumps need to achieve a COP of around three before their CO2 emissions become less than using natural gas. In countries like France and Norway with nuclear and hydro electricity, respectively, COPs are virtually academic, and heat pumps simply enable what is already low-carbon electricity to go further.
Meanwhile in the UK the Renewable Heat Incentive, which already applies to commercial installations, and Renewable Heat Premium Payments for domestic installations until the RHI also applies to them are market stimuli.
Daikin responded to the CO2 benefits five years ago with the introduction of its Altherma system for individual homes. Now the concept has been extended to larger-scale projects such as community heating for apartment blocks and commercial buildings.
Unlike the early Altherma systems for individual homes, the Altherma Flex air-source heat-pumps system is designed to deliver high temperatures of up to 80°C, making it ideal for refurbishment projects with existing radiators systems and to provide hot water at up to 75°C.
Achieving those high temperatures with an outdoor unit using R410A would require phenomenally high pressures. That problem is avoided by a 2-stage process using R410A to extract heat from the ambient air, raise its temperature, and deliver it to a refrigerant circuit. A second heat pump using R134a extracts heat from the R410A circuit and further elevates the temperature before transferring the heat to water. It must be stressed that this is not a 2-stage system but a cascade system.
The key to the operation of Altherma Flex is that the R134a units are associated with individual dwellings in an apartment block, individual businesses in an office development or individual heating zones. The R134a units can be compared with the heat-exchange units that are often associated with central boiler plant in such buildings.
That comparison is a little superficial, however. With central boiler plant heat is obtained by reducing the temperature of the water in the primary circuit — sensible heat. With Altherma Flex, heat is obtained from the R410A circuit by a phase change of refrigerant from gas to liquid — latent heat.
Outdoor units are available with heating capacities from 22 to 45 kW in five sizes, and units can be connected to deliver higher outputs of up to 500 kW. Up to 10 indoor units can be connected to an outdoor unit.
Indoor units are available with heating outputs from 5.5 to 16 kW and can be configured in a centralised or decentralised arrangement according to the requirements of the building. There are 10 models.
In a centralised system, the indoor units can be located in a central plant room. Indoor units are modular, so a system can easily be scaled up to meet large demands.
In a decentralised system, the Hydroboxes (indoor units) are located in individual dwellings such as apartments or collective housing. Each indoor unit can be operated independently to provide each property with its own control of heating and hot water.
Individual dwellings can also be equipped with separate tanks for domestic hot water. They are designed to stack on top of the indoor unit, which has a footprint of less than 0.6 m2. There are two sizes of unvented stainless-steel water cylinder — 200 and 260 l.
It is evident that the overall COP of each end circuit depends on the temperature the R134a unit is expected to deliver.
Aside from carbon-saving benefits and avoiding the complexities of centralised boiler plant, Daikin has identified several other benefits of the Altherma Flex system in the form of improved energy assessments.
One of the benefits is that for community heating solutions a centralised Altherma Flex system will attract a higher SAP rating.
Another benefit is the for apartments assessed against the Code for Sustainable Homes, the system will help achieve Code Levels 3 and 4, which is required in London.
Finally, for commercial buildings, the system qualifies for high SCoP values within SBEM calculations and will achieve BREEAM points.
It is also accepted by UK National Methodology Calculations that community heating with centralised plant is more efficient than individual systems.
How should the heat be charged for?
Daikin’s suggestion is that each indoor unit and outdoor unit should have its own electricity meter and the energy consumption of the outdoor units allocated according to the electricity consumption of the indoor units. A better way is using Daikin’s software tool to calculate the correct share of the running costs of the outdoor units for each apartment based on heat-meter readings.
