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BSEE M


Our methods might dier, but the heang and hot water industry shares the same ambions as the climate change protestors who recently brought city centres to a standsll, according to Steve Addis, product manager of boiler, water heater and heat pump company Lochinvar


ass protests on the streets of London and hundreds of other cities have tried to re-focus politicians’ minds


on climate change. The protestors fear that we are ‘sleep walking’ into disaster because of major distractions like Brexit.


They want to see real, practical action and should take heart from a recent report published by the highly influential parliamentary Committee on Climate Change (CCC), which highlighted the important role low carbon heating is playing in helping the UK reduce its dependence on fossil fuels.


The activists should also note that the UK’s total gas consumption has fallen by a hugely impressive 20 per cent since 2000. A range of factors has contributed, but improvements to heating and hot water technologies have been significant and the CCC particularly highlighted the potential of heat pumps.


Being able to take a flexible approach to the design of both heating and hot water systems is the key. The use of condensing technology means that many gas-fired heating and hot water products have already reached their maximum level of efficiency. Increasingly, we will need to adopt a system approach with designers making greater use of integrated and hybrid systems in which conventional and renewable systems are combined to hit more ambitious targets.


Demand ‘ This type of


integrated or hybrid soluon is a good way to keep inial capital outlay relavely low





Heat pumps have seen a surge in popularity in homes in recent years, but many are installed with back up from immersion heaters to ensure they are able to deliver hot water in the coldest conditions and when demand is high. This approach is not always practical in commercial buildings where hot water demand is much higher and because of the need to store water at 65°C to avoid the build-up of legionella bacteria. In order to stay within closely controlled budgets, specifiers often revert to tried and tested methods of providing heating and hot water by using traditional gas-fired methods. However, they can also use heat pumps or solar thermal in the same system with the gas-fired systems as back up for times of highest demand. This reduces running costs, but also has the added benefit of extending the operating life of the equipment. This type of integrated or hybrid solution is a good way to keep initial capital outlay relatively low and means some end clients, who might previously have considered renewables to be beyond their budget, can afford a renewable element. This may also help them satisfy planning requirements, meet their CSR obligations… and cut carbon. Until recently, it was hard to make a commercial case for a heat pump in a straight comparison with condensing gas-fired boilers in UK weather conditions. On a cold winter’s day, the carbon impact and the energy cost were likely to favour the boiler when compared with an electrically powered ASHP.


10 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MAY 2019


ADVERTORIAL: COVER FEATURE


Integrated approach will be crucial to low carbon future


However, one particular technical advance is tipping the argument in favour of heat pumps: ‘economised vapour injection’ (EVI).


Systems that use EVI have a much more efficient refrigeration cycle because the compression process is separated into two stages within a single compressor. As a result, most of the refrigerant is cooled during compression, which reduces the electrical energy consumed. This is particularly beneficial at lower evaporating temperatures, i.e. when the outdoor air temperature is around 0°C or below. It also increases the evaporating effect – the useful amount of heat that the refrigerant can extract from the outside air.


In applications where the building relies on electricity from the Grid, there is an even greater advantage in operating a modern ASHP at even lower temperatures, and it is significantly more carbon efficient than using other fossil fuels, such as oil and coal.


Gas Absorption Heat Pumps (GAHP) also have potential and are capable of delivering impressive gas utilisation efficiencies (GUE) of 140 per cent compared with an average of 96 per cent for boilers. Their efficiency is also less affected by changes in outdoor temperature. A gas absorption system will only lose around 10 per cent of its operating capacity when outdoor temperature falls from 5°C to -5°C, but an equivalent electrically powered heat pump may lose more than 30 per cent .


Control


GAHPs work particularly well if they are integrated with condensing boilers to provide low temperature hot water for underfloor heating or low temperature radiators, and the use of weather compensation control in the heating mode will also significantly enhance system efficiency. GAHP’s can also be


used to supply pre-heated hot water to a gas-fired condensing water heater They can be used as part of multivalent systems that can receive heat from a variety of sources. However, in such systems, the use of a suitably flexible and properly sized thermal store becomes the critical element. If the system is sized and controlled correctly, this will ensure the non-renewable plant only runs when required, so minimising fossil fuel use. The use of a thermal store capable of accepting multiple energy sources, in tandem with the latest heat pump technology, allows the design engineer to provide an extremely flexible, but high- output solution. The thermal store acts as a large, low-resistance header that can accept heat from up to three sources. This smooths out the system capacity to maximize efficiency. It also reduces legionella risk because it does not store domestic hot water for long periods. Ideally, the store should be sized to provide 20 litres per kW output from the heat pump, plus an additional 10 litres per kW output from the system boiler. This approach is not particularly challenging in a technical sense, but it does require proper pre-planning and assessment of the usage patterns within the building and, therefore, the likely best configuration for the system. Integrating technologies in this way requires good control strategies and a proper commissioning period to ensure the various parts of the system work in correct sequence. The system should be set up to ensure the renewable technologies are the first to respond to any call for heating and hot water, with gas-fired boilers acting as back-up and firing only for periods of particularly high demand.


This is just the kind of practical action climate change activists should be delighted to see.


www.lochinvar.ltd.uk Read the latest at: www.bsee.co.uk


uIntegrang technologies requires good control strategies and a proper commissioning period to ensure the various parts of the system work in correct sequence





In applicaons


where the building relies on electricity from the Grid, there is an even greater advantage in operang a modern ASHP





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