AIR CONDITIONING Stuart Eagleton
Making the right connections with DX kits
Stuart Eagleton, sales director at Fujitsu General Air Conditioning UK, discusses the advantages of adding cooling and heating to third-party air handling units.
T
he simplest solutions can sometimes off er the biggest benefi ts and Fujitsu’s DX Kit certainly falls into that category. By enabling the connection of air conditioning products to third-party ventilation systems to provide both cooling and heating, it allows us to make the most of HVAC system design. A growing awareness of the importance of indoor air quality has led to increased demand for eff ective ventilation. Any mechanical ventilation system will experience a degree of energy loss as stale indoor air is removed and cold or warm air is introduced, depending on the season. The resulting energy losses would previously have been mitigated through the use of thermal wheels or mixing chambers, but many such features were disabled following updated advice around centralised ventilation systems in the wake of the Covid pandemic. This has meant an increased load requirement for cooling or heating of the air supplied into a building, leading to higher energy consumption and a bigger impact on the environment. While this demand may previously have been met by chilled water circuits or gas boiler systems, advances in DX technology now allows equipment such as the DX Kit to off er a unique operating range which allows the removal or signifi cant reduction of pre-heat and frost protection, delivering operational cost savings and environmental benefi ts to support eff orts to decarbonise the built environment. Let’s examine some the key features in detail:
No need for pre-heat
For specifying an air conditioning system, the minimum room temperature for heating would be around 16°C to maintain a balance between
34 October 2023 •
www.acr-news.com
indoor and outdoor temperatures. If we think of an AHU heat exchanger as the indoor unit and the ambient air temperature entering the heat exchanger when operating in heating, this would often be below 16°C, putting the system at the limit of its operational envelope. The standard rule of thumb is that the entering ambient air can be as low as 10°C. Anything below that and the system becomes inoperable or some kind of third-party pre-heat device would be needed for frost protection or to raise the air temperature. This would usually involve an electric heater element at
considerable operational cost. The DX Kit, however, can operate with an entering ambient air temperature down to -7°C, which means the expensive pre-heat can be removed completely or, if the design requires operating to lower ambient, reduces the overall operational cost signifi cantly.
This is possible thanks to an improved system
control logic that allows condensing temperature to increase, maintain high heat exchange ratios and maintain suitable suction temperature rather than having negative eff ect on the refrigerant cycle.
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