Tomorrow and the BBC are filming at Penrhyn Castle on a project we have been working on for well over a year now. The project in outline is simple one which is to harvest heat from the waste water for re use. There was a Biomass project in the Lake District which got me thinking about this. At this campsite we heat up about 10,000 litres of hot water in a large tank which is all used in the popular sites showers in the morning. This very warm water is then flushed down the drain and goes to the sewage treatment plant. What a waste! But this is the same for almost every house, hotel and business in the world. No matter what generates the hot water and how green it is, a wasted KW is a waste KW. The questions for a research project is around how can we harvest this waste heat from showers, sewage, dish washing, clothes washing and so on in an economical and practical way.
The National Trust have been looking at this very question and teamed up via the Dwr Uisce project with Trinity College in Dublin and Bangor University here in N Wales to investigate. Can we harvest energy from our waste water? Penrhyn Castle generates all of its heat from a biomass district heating system. 25% of its electrical needs are met by the on site solar PV system. The biomass and generated electric are used to make hot water for the flats, offices, catering and toilets. All of the waste water from these systems go down the hill to the septic tank. The researchers have been spending the last year monitoring where this heat is, how much and where would be best to harvest this heat. Based on the Lake District campsite experience I had a theory about the septic tanks but we soon realised because of the distance from the castle that most of the heat was lost by the time it reached the tank. Following lots of monitoring the best place at Penrhyn is under the kitchen in the cellar as the water here has the highest temp and volume of hot waste water and therefore use. (the water is up to 60c when leaving the sterilisers and dishwashers) the next question is how and what impact will this harvesting have eg on grease management in the wastewater (eg will is settle in the pipe before the grease trap?)
The Universities have come up with three different approaches. Copper pipe in pipe harvesting. The hot water going into the kitchen is next to the waste water leaving the kitchen and thus could exchange heat (theoretical 26% efficient) or pushing the waste water through a buffer tank which is theoretically 36% efficient or a combination of both. The research is also looking at putting this harvested waste water then through a heat pump to gain even more heat. The systems are still being bench tested in Dublin at the moment but also looking at the grease impact to see if it settles earlier in the pipe inside the castle thus blocking the waste pipe. This factor is currently being bench tested. The equipment will be installed in the coming months to test real world use vs theoretical estimates. There are a few off the shelf large systems which are ideal for new large-scale sites that we could use today but nothing at this scale and also retrofit in such a sensitive building