ENERGY SAVING
Whilst the success of the NABERS concept has been acknowledged and is currently being developed in the UK, there are a number of elements that are highlighted and related to HVAC system application and design potential. Rather than simply designing to Part L related targets, simulation of operational performance would be required under different environmental scenarios. This means that the designer will need to completely understand the system in question in terms of control or work closely alongside a manufacturer to obtain true simulation results. Currently the demand for heating in
buildings and industry across Europe outweighs that of cooling but this is expected to change in the future with as much as a 72% increase in cooling demands by 2030. The potential to recover energy is now at the forefront of everyone’s minds, especially when designing for performance, expanding the use of heat recovery processes through VRF and multi- functional four pipe chillers. Air conditioning systems typically move energy from one space to another, for
the energy removed from rooms operating in cooling mode and rejecting in rooms operating in heating modes, rather than rejecting outside.
Example of the design potential of air conditioning. A VRF heat recovery system connected to both and AHU and fan coil units.
4 pipe chiller producing hot water and cold water simultaneously with no energy rejection to atmosphere. Domestic hot water made available via heat exchanger in hot water store.
example, removing heat energy from a room and transferring that energy to the ambient air using refrigerant as a transfer medium. Energy is consumed by the compressor and fan operation, with the ratio of energy consumption to energy produced used to calculate the systems efficiency. The higher this ratio the more efficient the system and the lower the cost of operation. To minimise a building’s operating costs,
we need to generate as many different uses from one piece of equipment as possible, understand its design potential and utilise a control strategy that will be optimised for efficiency gains. Using the energy removed from one process and utilising in another is a core component in achieving this. A Heat Recovery VRF can be very efficient when installed with typical fan coil units, using
This, in principle, increases the amount of energy provided in ratio to that of the energy consumed, (Cooling capacity + Heating capacity)/Power Input. This type of energy saving is maximised in the UK during the intermediate seasons of spring and autumn, when the building uses the system in mixed mode to satisfy different requirements. If we apply this to the various simulation methods adopted whilst designing for performance, benefits will be found in these intermediate seasons, but what about the rest of the year? We can extend this further when we start to think on a bigger picture by linking systems together. Providing direct expansion solutions inside air handling units for preheat, supply air tempering, maintaining extract air temperatures for thermal wheel operation or dehumidification processes can extend a typical VRF system. Constant cooling loads through supplementary data centre cooling will also expand the recovery potential across the year,
increasing a buildings efficiency. While we have been discussing space heating and cooling in relative terms, an important factor to take into consideration when trying to improve energy savings is the hot water that will be consumed, either by potable hot water or in industrial processes. Multi-functional four pipe chillers allow dynamic design potential for providing both cooling and heating operations simultaneously in a similar energy recovery method to that of VRF. Providing hot or chilled water to multiple sources operational potential can be expanded even further. By using a third heat exchanger, either within the chiller or placed within a thermal store, energy to produce domestic hot water can also be utilised. This adds an efficient bivalent source to a traditional boiler or removing the need for a boiler altogether. Even in the height of summer with the majority of services requiring cooling, we can still recover energy to serve the demand for hot water.
One of the key success factors of designing for performance is an intensive commissioning and fine-tuning process. It is important to remember that no matter how good the design, if the building is not commissioned correctly, it will never achieve performance targets. Largely involving control strategies, complete knowledge and understanding is pivotal. Engineer training through formal routes and manufacturer courses is key, but manufacturer involvement throughout the entire design and commissioning process is critical, especially when designing systems on various thermostat hysteresis or varying heat exchanger temperatures. Is designing for performance the way to
increased energy savings? From studying the Australian NABERS model, it would certainly seem so, but manufacturers expertise remains crucial to expand even further.
Office energy intensity by EPC, showing wide variation in rating and energy intensity. (source - BBP Design for Performance)
www.acr-news.com January 2020 43
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