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GOING RETRO WITH CHP What are the key considerations?
CHP technology working in conjunction with a condensing boiler and/or water heater can significantly improve the energy performance of a commercial building, whilst also reducing energy overheads for the occupier. However, when retrofitting a CHP system, what should you consider? Paul Wilson, National Sales Manager at Remeha CHP, explains.
A .
recent survey by the Telegraph and YouGov found that energy costs make up a substantial part of many companies’
budgets. One-fifth of those surveyed admitted to spending more than £250,000 on energy a year, while a quarter spent more than £100,000 per year1
With spending at such high levels, businesses are turning to new and innovative technologies such as combined heat and power (CHP) to reduce energy costs and increase profitability.
CHP systems burn natural gas to generate heat, while providing electricity to supplement or replace the grid supply. By generating electricity on site at gas prices, energy bills can be reduced by around 20% compared to conventional power generation2
. Also, in comparison
to purchasing from the grid, CHP electricity doesn’t suffer losses caused by moving power over large distances, resulting in a more efficient process. It is possible to install CHP into existing buildings and integrate it with existing boilers and water heaters. Before any work can be completed, however, it is good practice to audit the building to verify that CHP is the right solution and ensure maximum benefits can be realised. This should include, but not be limited to: checking the fabric of the building provides adequate insulation; ensuring the pipework is correctly configured and in good condition; testing water quality; and configuring the Building Management System (BMS).
Essential checks
The first port of call should be checking the fabric of the building is adequate so that the heat generated by the CHP unit is not lost. For example, the levels of heat loss experienced by older brick buildings with single glazed windows and little insulation would detract from the energy savings delivered by a CHP unit. In these cases, the priority should be bringing the building up to scratch by installing double or triple glazing and cavity wall insulation.
As CHP is used in conjunction with complementary heating technology, such as boilers and water heaters, it is crucial to get the pipework right so that all components work together properly. In a properly designed and
commissioned hybrid system, pipework should be configured correctly so that return water to the condensing boiler is not preheated. This approach ensures that the CHP serves as the lead heating appliance, and that the boiler recovers both sensible and latent heat from the flue gases. However, lack of space can often be a barrier in achieving correct pipework, so it is worth taking the time to assess whether the plant room can accommodate the necessary layout changes.
Correct sizing
In addition to pipework design, the CHP unit should be sized correctly in order to meet baseline heating demand. This ensures that the CHP operates 24/7 so it is continually generating low cost electricity and thermal energy. Some specifiers and consultants tend to follow the ’10 per cent for luck’ rule, which can lead to the installation of an oversized system. A better rule to follow is that no heat demand equals a CHP system that is not running – and without that, the anticipated electricity will not be generated.
Remeha provides assistance with this process by carrying out feasibility assessments which determine whether the base load for heat and electricity is high enough to keep the unit operational. For example, on a R-Gen 50/100-CHP unit the heat produced is around 100kW (depending on the return temperature to the unit) and the electrical output is 50kWe. If the base load is above these figures, the CHP will run continuously, supported by boilers if necessary, and both the heat and electricity generated will be used within the building.
In terms of pipework quality, older cast iron or copper pipes can corrode and pollute system water with contaminants such as silt and sludge. These contaminants can build up inside water storage tanks and collect around certain components, impairing system performance and adding to maintenance costs.
Flushed with success
uBefore any CHP installation, it is good practice to audit the building to verify that CHP is the right solution and ensure maximum benefits can be realised.
18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER OCTOBER 2017
In an ideal scenario, the entire system should be flushed before the CHP system is installed so that system water is as pure as possible. Periodic flushing of the system thereafter will also remove build- ups but this sudden application of pressure can cause leaks in weakened pipework. This is why its condition should be assessed before a CHP system is installed, and to prevent contaminants from circulating in the first place by implementing an appropriate water quality maintenance regime. For example, fitting a magnetic sediment filter at the point of entry minimises the build-up of silt and sludge. Finally, the capabilities of the BMS should be assessed to ensure it is
uThe Remeha R‐Gen Combined Heat and Power (CHP) range is the sustainable solution to providing highly‐efficient heat and power for applications with consistent heating and electricity.
compatible with the CHP. If so, the system must first be configured by the BMS provider before it can be used for automated control. However, as it is an emerging technology, some older software is not CHP compliant. In these cases, a total replacement may be necessary.
As energy costs continue to be a pain point for UK businesses, CHP can offer a long-term, sustainable solution. Although, for these benefits to be realised, it is important that the building is properly audited and the CHP is sized correctly for the overall system.
remeha.co.uk Sources:
1
http://www.telegraph.co.uk/ business/ready-and-enabled/ benefits-of-energy-saving-measures/ 2
https://www.gov.uk/guidance/ combined-heat-and-power
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In terms of pipework quality, older cast iron or copper pipes can corrode and pollute system water with contaminants such as silt and sludge. These contaminants can build up inside water storage tanks and collect around certain components, impairing system performance and adding to maintenance costs.
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