Modern Building Services

20 MODERN BUILDING SERVICES NOVEMBER 2021 NET ZERO I n the drive to decarbonise our towns and cities, renewable technologies are making significant inroads into the supply of heat for commercial buildings. The UK Government’s 10-point Plan for a Green Industrial Revolution highlighted the challenges of making buildings more energy-efficient by moving away from fossil fuel boilers, and heat pumps are often well equipped tomeet the demands for space heating. Delivering potable hot water to those same buildings, however, presents a different set of hurdles to overcome. Improvements to the fabric and air-tightness of buildings, due in part to the impact of Building Regulation Part 2LA, MinimumEnergy Efficiency Standards and building certification schemes such as BREEAM, mean that space heating loads are often reduced, while the hot water demand remains constant, leading to concerns over the potential environmental impact. CO 2 hot water generation One of themain issues in replacing traditional fuels with heat pumps for potable hot water use is the maximum temperature achievable froma single stage refrigerant circuit. For R410 this is approximately 55°C, for R32 and R134a it is 65°C. This is generally at a system’s maximumoperating capability with efficiency impacted accordingly. Using natural refrigerant CO 2 , which does not fall under F-Gas regulations, MHI’s Q-ton has been developed to produce hot water ranging from 60°C to 90°C even down to -25°C ambient, so when applied into commercial buildings requiring 70°C leaving water temperature to combat legionella, system efficiency is maintained. The ability to hold capacity to low ambient temperatures also helps with reducing capital costs by ensuring the kW capacity needed is supplied all year round without the need for electric immersion heater back-up. Unlike systems using gas or oil, renewable heating systems are not usually designed for instantaneous hot water and so variation in design is required. A system incorporating a product such as the Q-ton needs to be designed to meet a building’s peak load. Using a method known as energy accumulation, the energy is generated, and a thermal store is used to hold the hot water until it is ready to be used. Understanding profile It is important to fully understand a building’s usage profile in order to design effectively, working on the basis that enough energy is required to meet peak load, but with enough heat pump capacity to replenish that energy before it is required again. This process is fluid, with the likelihood that water is being used in some aspect throughout most of the day. It is also important to consider any possible reductions in operating costs by designing a system to operate during periods of low electricity tariffs. From a design perspective, the system needs to be capable of providing sufficient hot water between the thermal stores and the Q-ton together to meet demand of the absolute peak load. The Q-ton then needs to be able to heat enough water back to temperature from what has been used in order to meet the next peak with the process continuing throughout the day. Therefore the relationship between the volume of stored water and an the system kW capacity is based on the building’s usage pattern. FEATURE NET ZERO Harriet Evans , MHI Sales Director at Beijer Ref UK & Ireland, discusses why the requirement to produce potable hot water from renewable technologies shouldn’t be ignored. Why use gas: renewable methods of producing potable hot water