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Air conditioning
Unlocking the potential of HVAC systems
Martyn Ives, distribution sales & technical services director at Fujitsu General Air Conditioning UK, explains how providing heating and cooling to ventilation systems from an air conditioning product can reduce energy losses
E
ff ective ventilation in our buildings has never been more important, while soaring energy costs and the drive to decarbonise
our buildings place even greater emphasis on the need to realise the full potential of an HVAC system through careful planning at the design stage. Any form of mechanical ventilation will suff er a
level of energy loss as the indoor environment is removed through fans extracting stale air, while cold or warm air is introduced depending on season. The resulting energy losses would previously have been mitigated through thermal wheels, or mixing chambers, but since advice about operating centralised ventilation systems post covid, many of these features have been disabled. This change has led to increased requirements
for cooling or heating air that is supplied into a building, leading to an increase in energy consumption and a higher impact on the environment. The Fujitsu DX Kit, recently named Industrial/Commercial Air Conditioning Product of the Year at the HVR Awards, is a simple yet comprehensive solution that works by providing heating and cooling to ventilation systems from an air conditioning product.
Parallel piping of EEV units
Using electronic expansion devices provides the benefi t of being able to close off a refrigeration circuit, by simply driving the valve closed; it is not possible to do this with a thermostatic
valve because it is self regulating. Utilising an electronic device means that staging of cooling or heating capacity is possible across multiple heat exchangers, giving greater control and improving system effi ciency. It also means that multiple air handling units (AHUs) or ventilation systems can be served from a refrigerant system, reducing capital costs and installation space. Electronic expansion devices are generally limited
to only allow 25kW cooling capacity, which means that the maximum heat exchanger capacity within an AHU or ventilation system would be 25kW. An exclusive feature from Fujitsu is the ability to connect two EEVs in parallel to provide 50kW from one heat exchanger while maintaining complete controllability; in essence, expanding the application and associated benefi ts across a wider range of applications.
Operation without pre-heat
When specifying an air conditioning system, we would normally note that the minimum room temperature for heating would be circa 16°C to maintain a balance between indoor and outdoor temperatures. However, thinking of an AHU heat exchanger as the indoor unit of an air conditioning system, and the ambient air temperature entering the heat exchanger when operating in heating, this would often be below 16°C, therefore moving the system out of its operational envelope. The standard rule for this type of application is that the entering ambient air can be as low as 10°C. Below that the system is inoperable or some kind of third party pre-heat device is required for frost protection or to raise the air temperature in line with guidance – usually an electric heater element which can prove costly to operate. Met Offi ce data shows that there were fi ve months throughout 2020 where the maximum mean temperature was below 10°C in England (Nov – Mar) giving an insight into the extent that a pre-heat would be used. Fujitsu DX systems continue
to operate with an entering ambient air temperature
Above: Martyn Ives, distribution sales & technical services director at Fujitsu General Air
down to -7°C. This means that an expensive pre- heat can be removed completely or, if the design requires operating to lower ambient, reduces the operating costs signifi cantly. This is made possible by an improved system control logic that allows condensing temperature to increase, maintain high heat exchange ratios and maintain suitable suction temperature without hyper condensation.
Heat recovery
We know air conditioning or refrigeration to be a process of moving energy from one place to another. Normally we associate this with removing heat energy from a room that is operating in cooling, transferring it through the refrigeration circuit and expelling outside, vice-versa in heating. Once this energy is rejected, it is lost from the system. However, through heat recovery methods, the energy removed from rooms in cooling can be reused in rooms that require heating. When we apply heat recovery application to this type of design it means that we can remove energy in one heat exchanger, cooling the air and lowering relative humidity, then transfer that energy through the refrigeration circuit and reintroduce it via the subsequent heat exchanger operating in heating. The only power requirement from a compressor point of view would be enough to provide the cooling side of the system – heating would be provided at little or no extra cost. The scalability is endless and could lend itself to
pre-heat coils, localised re-heat terminals, other AHUs, air conditioning fan coils and water heating products. It’s all about making the most of our HVAC
systems. DOWNLOAD THE HVR APP NOW December 2022 23
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