Combined Heat and Power (CHP) will work well for many building applications, but which are the most suitable projects and why?
The need to address energy use and carbon dioxide emissions resulting from the operation of buildings is being driven by tightened legislation, planning policies and building regulations. By capturing heat, that would otherwise have been wasted in conventional centralised electricity generation; on-site Combined Heat and Power (CHP) offers a means of generating local thermal and electrical power. In doing so, CHP reduces carbon dioxide emissions and reductions in primary energy use (the fuel), ensure real cost savings.
CHP is suitable for applications where there is a simultaneous demand for electricity and heat for a substantial period of the year. To be financially viable, a unit needs to operate for at least 4,000-5,000 hours a year. Operating even longer than that will see increased economic benefits and further reduced emissions.
Large scale applications
The financial and environmental case for CHP is strongest for applications where there is steady and continuous demand for heat and electricity. Large industrial sites, such as paper mills, chemical and refining plants, and food and drink processors – particularly those in 24-hour operation – can make significant financial savings with CHP. With a thorough understanding of heat and electricity demand for the particular industrial process, a CHP plant can be correctly sized in order to maximise running time, as well as increasing financial and environmental benefits.
Hospitals, as large facilities in 24-hour operation, are ideal for CHP. They have to be maintained at relatively high ambient temperatures at all times and they have substantial demand for hot water. The energy use patterns are predictable, making accurate sizing of CHP relatively straightforward.
Universities and their campus buildings are also well suited to CHP, particularly where the same system heats teaching and office areas, which have heat demand throughout the day and into the evening. CHP can be applied to heat on-site accommodation, which typically has its highest heat demand early in the morning and in the evening. Universities also have a high demand for electricity, with widespread and dense IT use.
CHP will operate successfully in community heating and district heat networks that provide heat and electricity to a diverse, but proximate group of buildings. The different usage patterns of the buildings, which may include commercial units, public buildings and dwellings, provide the mix of heat and electricity demand necessary to make CHP viable.
A key consideration here is the likely change in demand and usage patterns as additional buildings are added to the district heat network. Sizing decisions must take account of this, and as a result, the CHP plant may be slightly oversized at the initial stages of the network.
Commercial and small-scale applications
CHP can also be used in commercial and small-scale applications. Swimming pools have continual need for heat to maintain their temperature, coupled with a high demand for electricity to operate pumps and water treatment equipment. Similarly, leisure centres also have long opening hours with a substantial demand for hot water throughout.
Commercial applications can also benefit from smaller CHP installations. The combination of different usage patterns for bedrooms (with high water demand), public areas and ‘back of house’ makes it possible to run a CHP for long periods of time, maximising its benefits.
Small-scale applications are typically residential buildings (50 - 200 dwellings)
Analysing demand: the key to success
The key to a successful CHP installation – at whatever scale – is to identify the electrical and heating loads, and their level of congruency, in order to model the energy usage and optimise the size of the CHP unit. Too small a unit and the project will not maximise heat and electricity generation, but an oversized unit will either run part load, or not run for a sufficiently high number of hours to give the intended financial and environmental benefits. Surprisingly, the latter (oversizing) is the more common issue in the building world today
CHP is suitable for any building applications where there is a simultaneous demand for electricity and heat for a substantial period of the year, and will provide both financial and environmental benefits.
All industrial sites, whether large or small, particularly those that operate for 24-hours, can make significant financial savings with CHP.
CHP will operate successfully in district heat networks that provide heat and electricity to a diverse, but proximate group of buildings such as commercial units, public buildings and dwellings. The different energy patterns and the combination of heat and electricity demand make CHP a very viable solution.
Mid and small-scale applications such as universities, swimming pools and residential homes, can all benefit from a CHP installation.
- At whatever scale, a successful CHP installation is dependent upon a knowledge of electrical and heating loads, and their synchronisation, in order to model its energy usage and optimise its size.
After considering whether your building application can benefit from a CHP system, learn how to draft a high quality specification for your system to get the most out of your cogeneration project.
Read The ENER-G High Quality CHP Plan.
Topics: CHP / Cogeneration