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CONSIDERATIONS FOR HEAT RECOVERY INCLUSION The start of the process would be to determine the client requirements or application of the recovered heat , and then to determine if the need will be practically sourced from the refrigeration or air conditioning system . It must be noted up front that some applications , particularly in processing or industrial applications , cannot be met by heat recovery alone . In those cases , a combination of heat reclaim system with alternative heating systems such as boilers become attractive .
“ If a client wants to wash down their facility as an example with 70 ° C water , and the ( ammonia ) refrigeration plant is located 400 meters from the factory floor , it ' s going to be energy and capital intensive trying to reach those temperatures that may require high discharge pressures and high pumping cost . That in turn makes the system very inefficient so you defeat the purpose of trying to harness that energy ,” says Petrie van der Merwe , senior mechanical engineer – industrial refrigeration at Energy Partners Engineering .
In most cases , each installation and system would be unique and so the considerations would be varied . In order to get to the required end result , each design would have to consider options in refrigerant choice , suction and discharge pressures , use of high quality – and low-quality waste heat and account for different heat losses in the system .
Van der Merwe continues , “ The other major considerations in heat recovery are to evaluate and understand the profile of the heat load that the client requires for their facility , timelines and volumes . This could be a continuous draw-off as you find in a hospital or hotel , a batch production application where you use 100 kilolitres of water over a specific time of the day , or a washdown cycle . The load profile and the logical interfaces for heat reclaim will then determine the system design . In an industrial refrigeration system , the heat reclaim interfaces would ( mostly ) be from two areas , being the de-superheating of the compressor discharge or the compressor oil cooling circuits ( if present ).”
Heat recovery can be achieved through several types of heat exchangers based on system design characteristics . Some of the more common types include shell and tube , plate , condensers , evaporators , and even boilers . Depending then on the type , heat transfer can occur in gas-to-gas , liquid-to-gas , or liquidto-liquid forms . Other important factors of the particular heat exchangers design characteristics include material types , transfer mechanisms and flow configurations .
When installing a heat recovery device , placement is extremely important too . “ Considering de-superheating as the source ( which is a relatively simple process ), heat recovery
RACA Journal | Benjamin Brits Danfoss
devices need to be placed at the very highest point in system piping . If the discharge gas starts to condense in the heat exchanger , it is critical that the liquid drains to the condenser rather than the compressors , which will obviously have serious implications . The circulation on the secondary side of the heat exchanger depends on the system design – the secondary pumps could simply circulate through some type of buffer tank , circulate directly to the site or alternatively tie into a second heat exchanger , with tertiary pumps connected to a process in the facility ,” van der Merwe adds .
He continues , “ Heat recovery gets a bit more intricate in oil cooling circuits . This method can be used when the plant is equipped with screw compressors . The oil cooling circuit
A complete heat recovery unit .
Large domestic hot water tanks installed at a food manufacturing facility using heat recovery from an ammonia plant .
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