Mini chP hEalTh cENTrE rETrofIT cARe PAckAge CHP is ideal for healthcare centres but only if systems are designed and commissioned properly. SenerTecs Gary Stoddart looks at lessons learned in Cumbria C HP has an important role to play in improving the efficiency of buildings, particularly those with high and continuous heating loads, such as healthcare buildings. This is because CHP operates most efficiently during long running hours. Less stopping and starting means less wear on the engine, reducing maintenance costs and downtime and making the system more efficient overall. Furthermore, with electricity from the grid both subject to transmission losses and costing three or four times more than that produced on-site, CHP can potentially be approximately 30% more efficient than traditional heating plant electricity (See panel, The economics of CHP). The 30% efficiency is based on savings made from electricity being produced by CHP using natural gas, rather than purchasing electricity from the grid, plus the generation of heat. For example, 15kW of heat and 5.5kW of electricity from the grid would cost an average of 1.37 (based on 14p per kWh for electricity and 4p per kWh for gas1), but only an average of 81p if generated via a Dachs 5.5 CHP unit, which requires 20.3kW of gas to produce the same amount of heat and power. eor RMadE cockErMouTh: ThE IMporTaNcE of chEck-ups This has been recognised in NHS and Sustainability a report to the House of Commons environmental audit committee by the National Audit Office (NAO) which said that CHP should be extended across healthcare facilities in a bid to cut costs by 180m a year.2 However, for CHPs potential to be realised, systems need to be correctly designed, commissioned and monitored. When assessing a site to see how feasible it is for CHP, we look at the base load for electricity and heat. For example, the heat produced on a mini-CHP unit the economics of chP CHP uses natural gas to generate electricity (with the combustion exhaust gases being disposed of in the same manner as with a boiler) to replace electricity drawn from the grid. With an energy cost ratio of around 3.5/1 (electricity 15p per kWh and gas 4p per kWh), the savings are calculated using the cost of energy input to the CHP unit (natural gas) and the value of the heat output (thermal) and the electricity produced. As an example, a mini-CHP unit operating 24 hours a day could save more than 10,000 a year and approximately 60 tonnes of CO2, but this depends on many factors, including energy costs and the efficiency of the existing heating system. by the CHP during the day, ready for the evening peak (say, 4.30pm to 7pm). If the heat cannot be used, the site will either have to dissipate (waste) it or shut down the CHP. We estimate that there are a large number of CHP units installed across the country that are not running as intended but this situation could easily be avoided through early discussions about system design, CHP sizing and effective monitoring. The integration of a mini-CHP at Cockermouth Community Hospital and Health Centre in Cumbria illustrates what can happen if the technology is not optimised. The BMS controls were not set correctly, which meant the boilers took lead heat generation for the system, which resulted in the CHP unit remaining in a standby position (see panel, Cockermouth: the importance of check-ups). Adjustments were made to the BMS system, reducing the system flow temperatures and allowing the CHP unit to take lead heat generation. The site is now recording significantly higher CHP running hours and benefiting from the resulting heat and electrical contribution to the building. This illustrates the need to be mindful of the building dynamics and of how the end user intends to use heat and power. CIBSEs AM12 urges designers to seek the advice of CHP suppliers at an early stage of the design. A timely conversation with the controls engineer is also crucial to ensure the BMS is set up with the CHP properly integrated. is typically between 12.5kW and 15.5kW depending on the return temperature to the unit and the electrical output is 5.5kW. If the base heating load is above these figures, the CHP will run continuously, and the heat and electricity will be used in the building which is the ideal. There is no minimal operational period per year that has to be met, but it is important to note that if a unit is not running it is not contributing towards payback. As there is no Feed-in Tariff available for electricity generated by gas CHP units above 2kW, the system should be specifically designed to ensure that all the electricity generated is used in the building. As a CHP unit supplements existing boilers and/or water heaters, the system needs to be designed and sized to ensure that the CHP is used first, and that the boilers and water heaters are used during peak periods. If a site has peak demands for hot water, storage is the best solution to keep the CHP unit running. Heat produced by the CHP over a period of 10 hours or more is stored in a preheat cylinder, and this hot water can be used during the peak period (for example, 6.30am to 9am). The cylinder will then be heated Putting an effective monitoring system in place can help you keep track of how CHP is performing. A modem, connected to a landline or mobile network, can transmit data between the site and the CHP units monitoring centre. The manufacturer should have the resource and expertise to analyse data in real time, and provide guidance on how to solve any issues or alter the system to maximise performance. Consideration should be given to availability of a long-term maintenance contract. CHP engines are maintained on a running hours basis; the maintenance period for the CHP at Cockermouth is 3,500 operating hours. If the mini-CHP unit is being remotely monitored through a modem, it will inform the end user and in this case SenerTec when a service is due. The firm is set to offer remote monitoring with every Dachs Mini-CHP unit. If CHP is to be more widely deployed across the healthcare sector, the importance of correct design, commissioning, monitoring and maintenance must be fully understood.cJ references CHP unit at Cockermouth Community Hospital and Health Centre 1 energy Saving trust: Calculations 2 nHS and Sustainability, NAO, 2015 cockErMouTh: ThE IMporTaNcE of chEck-ups Cockermouth Community Hospital and Health Centre in Cumbria was rebuilt in 2013, with the aim of accommodating the towns primary healthcare services under one roof. CHP was specified as part of an energy and carbon saving strategy to meet long-term environmental and BREEAM targets. A 5.5kW Dachs MiniCHP unit was installed to provide both hot water for general medical needs and electricity to supplement main grid supply. Initially, when integrated with the BMS, the CHP unit did not run as expected. The system operating temperatures for the heating system and the heating water flow rates were both set significantly higher than required. This resulted in system return temperatures in excess of 73oC. As a result, the CHP would only run for a MorE Read matter of minutes first thing in the morning and then stand idle for the rest of the day. When our business development manager Mark Gibbons visited the hospital, he quickly realised that the CHP unit had been running for only a fraction of the time possible. By reducing the boiler temperatures down by 1 or 2C we were able to operate the CHP as intended. The hospitals maintenance engineer reset the system pumps so that the velocity in the system dropped, increasing the flow and return delta T and reducing the return temperatures to the central plant room. The mini-CHP unit is now running almost continuously, meaning the hospital is benefiting from the carbon and energy savings the system was originally specified to deliver.