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WATER HEATERS PLUS CHP Adding value with the right mix


Often, it’s not just the individual components of a heating and hot water system that are important; a combination of products working together can also greatly increase efficiency. Here, Chris Meir (pictured), Sales Director at Andrews Water Heaters, explains why pairing a water heater and a CHP unit can make economic and environmental sense.


A


consistent supply of hot water is essential for all commercial premises and with pressure mounting on businesses to cut costs and reduce carbon emissions, engineers can add


value by implementing the right mix of technology to create the most efficient and reliable system design.


For premises with a high demand for hot water, direct gas-fired storage water heaters are a great solution. There are several different kinds on the market to suit the individual requirements of a property, such as whether the demand for hot water is sporadic or ongoing. Some have one burner, which gives them a high rate of recovery, and some have multiple burners to provide both high rates of recovery and built in redundancy. This means that each burner can work independently if the others fail, ensuring a more reliable hot water supply for end users.


However, if the circumstances allow for it, a CHP system installed alongside the water heater(s) can offer even greater performance, efficiency and long-term cost benefits. CHP systems burn natural gas to generate heat, while also providing electricity to supplement or replace the grid supply. By generating electricity on site, energy bills can be reduced by around 20% compared to conventional power generation1


. Economical


Using a CHP system, businesses can produce electricity at gas prices, which is cheaper than buying it directly from the grid, as electricity is approximately 8 pence more expensive per kW/h.2 Also, in comparison to purchasing from the grid, CHP electricity doesn’t suffer transmission losses caused by moving power over large distances, resulting in a more efficient process. By generating heat and power simultaneously, CHP can reduce carbon emissions by up to 30% compared to conventional methods1


. At the same


time, where the ‘waste’ heat from the generation process is lost at gas power stations, the heat generated by CHP can be re-used. To ensure an efficient and reliable hot water system, CHP can be used to pre-heat enough water to cover a building’s base load requirements, meaning the water heaters only fire to cover additional demand when the storage runs out.


uAndrews’ MAXXflo offers revolutionary self‐contained storage water.


Take a large hotel, for example, which has two peak periods per day; one in the morning (6-9AM) and one in the evening (5-8PM), where approximately 3,000 litres of water are used during each. If the CHP unit is sized correctly, it should run from 8PM for approximately 10 hours, with the water maintained at a 60°C temperature in a thermal store for when the morning peak period


begins at 6AM. As a rule, one Remeha R-Gen Dachs 5.5kW unit can feed one 2,500 litre cylinder – enough for approximately 83 average, five minute showers.


Then, when guests begin having their morning showers, the CHP unit will detect cold water entering the system and generate an additional 7/800 litres during the peak period. It will then re-fill the tank over the course of the day in time for the evening peak period, where the cycle begins again. At the same time, the water heaters are on hand to supplement supply, ensuring there is always a constant supply of hot water.


Hybrid system


An example of another application is a hybrid system involving two Remeha CHP units, a 750-litre buffer vessel and Andrews Water Heaters gas-fired water heaters, which played a major role in enabling the London Fire Brigade (LFB) to reduce its carbon footprint by 28% in six years. Using internal combustion engine technology, the Remeha R-Gen Dachs generates electricity while it is running and produces heat as a by- product, which is captured and used for water and space heating. At times of peak demand, for example in winter when additional heat may be required to maintain indoor temperatures, the BMS will automatically switch the CHP from supplying domestic hot water and divert it to supplement the heating circuit, with standby gas-fired water heating boosting hot water volumes. The entire Andrews Water Heaters range combines maximum efficiency levels with low NOx for economical running costs.


In just four months, LFB's station at Battersea received 4,100 kWh of electricity from the R-Gen Dachs and 1,730kWh from solar PV. The combined systems were calculated to reduce the site's carbon footprint by 13 tonnes a year. Battersea has reported a £2,500 annual saving on fuel costs. This means that the payback on the purchase cost of the CHP system could be less than six years. In all of these examples, the system is designed so that the CHP unit is running for 24 hours a day. To reap maximum benefits from both CHP and water heating units, correct sizing is of the utmost importance. This is because oversized CHP units will not run if the heat demand is not present, and thus the anticipated electricity will not be generated. The golden rule for CHP is to keep it as small as possible and to remember that properties with high and continuous, year-round heating loads, such as hotels, care homes and leisure centres, achieve the most efficient operation. Sizing the system so that the base load heating requirements can be met largely by the CHP unit alone will result in the continuous generation of low cost, low carbon electricity as a by-product of producing base load heating.


Oversizing


When calculating the size of the system, Building Regulations state that CHP must be sized to provide ‘not less than 45 per cent of the annual total heating demand’, which includes space heating and domestic hot water. This is critical for CHP as oversizing for summertime loads can result in either non-operation of the CHP, or the heat produced being ‘dumped’ in order to continue generating electricity.


It is also critically important to size the water heating unit(s) correctly. Too big and it will waste energy, too small and it will not produce enough hot water. Thankfully, help is available for this. The CIBSE Public Health & Plumbing Engineering guide parts G1/G2 provide assistance, but progressive manufacturers also offer helpful sizing calculation tools.


For example, the original Andrews Water Heaters Size-it tool was launched in 1996 to assist with sizing


16 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2017 VISIT OUR WEBSITE: www.bsee.co.uk ‘ By generating heat and


power simultaneously, CHP can reduce carbon emissions by up to 30% compared to conventional methods. At the same time, where the ‘waste’ heat from the generation process is lost at gas power stations, the heat generated by CHP can be re‐used.


’


uThe COMBIflo from Andrews Water Heaters is a range of condensing stainless steel water heaters that produce both hot water and heating from one cabinet.


calculations. The way it worked was simple – users enter their hot water requirements, depending on property type, to determine appropriate products that would meet their needs. The sizing guide recommended the system design to suit a building’s usage, hot water demand, fuel type and other specifications as well as a minimum temperature of 50 degrees Celsius, in line with the latest Building Regulations.


This spring, Andrews Water Heaters is releasing a revamped version of its Size-it tool which will be quicker, personalised and available on any internet-connected device, including tablets and smartphones. Users will be able to manage a portfolio of projects and tailor the sizing to their exact property type and hot water requirements. Size-it also provides links to the latest legislative guidance which can be easily downloaded as a summary or detailed report.


So, as energy prices and efficiency targets continue to be a pain point for many businesses, hybrid systems may offer the solution. Just as it is crucial to choose high quality components for a heating system, it is equally as important to consider how those components work together for maximum benefit. In many cases, CHP and gas fired water heaters make the perfect partnership.


www.andrewswaterheaters.co.uk


1. https://www.gov.uk/guidance/combined-heat- and-power


2. https://www.gov.uk/government/statistical-data- sets/gas-and-electricity-prices-in-the-non-domestic- sector


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