Waste Water Heat Recovery

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Information based on Recoup Waste Water Heat Recovery System.

Waste Water Heat Recovery on District Heating

The vertical nature of dense housing perfect for district heating, is also perfect for waste water heat recovery. This articles looks at how this affects efficiency calculations.

The following is taken from our heat network calculator...

Net77.png

The chart shows the energy use over a half decent heat network, included all losses. As you will note there is no mention of energy wasted down a plug hole.

As this is a loss, and makes up a percentage of the load, the energy down the plug hole, should really be shown in all energy allocation charts as part of the hot water load.

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 calculations treat heat down the plug hole 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 providing:

  • Showers are used instead of baths
  • Seasonal heat network efficiencies are over 80% (excluding waste heat recovery)
  • A waste heat recovery system such as the Recoup System is installed
  • A heat interface unit suitable for pre-heated mains water is used, such as The Data HIU