Commercial & industrial heating 1 Hotel case study
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feed into a manifold, which then distributes heat to the air conditioning, heating or hot water appliances. Each of the appliances has an optimum flow rate, depending on the demand. ‘You have to balance your system properly so that
each appliance gets the right amount of water and the system can operate with minimum energy loss,’ says Buetow. Very often at other sites, he adds, over-sized pumps are installed, which results in hot water running through the pipe network too quickly, so that its heat is not transferred to the heating space effectively and the return temperature is almost the same as the flow temperature. For standard heating zones, there needs to be a
difference of 10 to 15C between the flow and return temperatures to run the heating system at optimum efficiency, says Buetow. ‘You have to calculate the size of the pumps very precisely in order to achieve this.’ The heating system is adjusted to compensate for
changes in the outside temperature by raising or lowering the flow temperature of the water in the pipework. Buetow says this is much more efficient than the more typical scenario of leaving heating systems to run with the same water temperature regardless of the weather, as this causes them to be switched on and off more frequently. The hotel’s CHP system, from ENER-G, has a
500kW heat capacity and 384kW electricity capacity and is expected to run 6,000 to 7,000 hours a year to maximise efficiency. Gidon Rotem, chief engineer at the London branch of Electra, the M&E consultant for the project, says it is critical that CHP units are correctly sized so they are switched off as infrequently
Off-site construction saves time
The hotel’s 1,000-plus bathrooms were pre- fabricated off-site using the ‘pod’ system – which reduced construction time on the site by 14 to 16 months and greatly improved the build quality, according to M&E consultant on the project, Electra Traditional methods of bathroom construction
in hotels can lead to high levels of damage because so many trades have to converge on a small space, it says. By contrast, the pods are designed with the ducts and pipes attached to the bathroom and the fan coil is mounted above the pod ceiling. All the installation of the fan coils and pipework
took place at the pods’ factory. The shafts, pipes and ducts were manufactured and pressure-tested in Israel before being shipped to the pods factory in Newcastle, England. When the pods reached the hotel construction
site in central London, all that remained to be done was to make the vertical connections between the shaft’s pipes and ducts. The entire hotel was built in 27 months.
The absorption chiller uses CHP heat to produce cold water
as possible. This switching off, or ‘cycling’, greatly impairs efficiency, increases maintenance costs and lengthens the payback time for the unit. The optimum size is normally between 10% and 20% of the total heat demand, he says. The unit runs on gas and its primary purpose is to
generate electricity. Rotem estimates the CHP unit is generating 10% to 15% of the hotel’s total electricity needs. With the daytime cost of electricity from the national grid at 8p to 12p per kilowatt hour, and the cost of generating electricity from natural gas at only 3p per kilowatt hour, using the CHP unit makes a lot of sense. The payback period for using the CHP unit is reckoned at three years. The hotel’s biomass boiler has yet to be fully
commissioned. Dave Bell, chief engineer at the hotel, says the biomass boiler will be used and the delay is mainly due to the need to get other parts of the building up and running first. Bell is exploring the possibility of using dried food waste from the hotel as feedstock for the boiler. ‘We think we’ve probably got enough food waste to
run the biomass boiler for about 10 hours a day during the conference season [which runs 10 months of the year], and for about four or five hours a day when we just have leisure guests in,’ says Bell. He adds that the wood pellets are ‘not overly
expensive’ and could easily be bought in to supplement the feedstock derived from food waste. ‘We want to be one of the greenest hotels in London. We get a lot of enquiries from companies who ask about our green policies and we are winning business on the back of it, so it’s important for us.’ The absorption chiller, a 174kW capacity Broad X Non-Electric model, takes heat from the CHP and >
52 CIBSE Journal October 2010
www.cibsejournal.com
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