Waste Water Heat Recovery
Information based on Recoup Waste Water Heat Recovery System.
The following is taken from out heat network calculator...
The chart shows the energy use over the network, included all losses.
As energy down the plug is not counted as a loss, but rather part of the hot water load, accounting for it properly is not straightforward. As it is a loss, and makes up a percentage of the load, the energy down the plug, should really be shown in all energy allocation charts.
Here however we wish to best describe the benefit of installing waste heat recovery, and as such calculate a revised efficiency figure. If we were to adopt the approach that all calculation treat heat down the plug as an inefficiency, then it would involve a complete rework of many efficiency standards.
So, we feel a suitable method is to treat the recovered waste heat as an energy gain used to offset heat losses from the network.
Therefore, if the annual energy recovered from waste water is equal to the annual losses, then the system would be 100% efficient. For every kWh generated at plant, the same is used for hot water and heating - with no net losses.
It does make it possible for systems to have an efficiency greater than 100%, by recovering more energy than is lost in distribution. Achieving efficiency levels of 100% or greater could even form the basis of the gold standard in heat network design.
Is this possible ?
65% of heat can be recovered from showering.
Approximately 40% of energy use on hot water on an efficient network. 20% on losses.
If baths are used then showering will only account for 25% of water use. 0.65 x 0.4 x 0.25 = 6.5 % ...No
If showers are used pretty exclusively then 0.65 x 0.4 x 0.75 = 19.5 %
That is tantalizingly close to offsetting the losses, and would give us an overall efficiency of 99.5%
So, the answer is yes - efficiencies of over 100% can be achieved is showers are used instead of baths, and heat network efficiencies are over 80%.
