Greywater heat recovery v solar thermal

If you are inputting data into SAP you get more CO2 reductions from installing a greywater heat recovery system than a solar thermal system with 2m2 of flat plate collector. Leaving aside the fact that a 2m2 solar panel would be a particularly bad design decision – if you are going to install a solar thermal system then in my opinion it is a false economy to install less than 4m2 of panel – it still seems a surprising fact.

SAP penalises solar thermal systems with regard to overall CO2 emissions saved because most of the systems installed in the UK require a pump to transfer the heat exchange fluid around the system. And a pump requires electrical energy. Solar Energy UK states that solar thermal systems produce between ten and twenty times more heat energy than they consume in electricity. ( I assume that this is over the course of a year, and makes sense; in most solar thermal systems the pumps are small circulating ones set at their lowest speed. If the hot water back up is provided by an electric immersion heater, then the SAP calculations would provide the same story as the STA website, as SAP looks at CO2 (not energy) produced or saved, and in this case the energy source is the same. But, because electricity in the UK is currently about 2.5 times as carbon inefficient as gas, then if you are displacing gas from a condensing boiler, then the figures would be different. In such a case the solar thermal system would save 4-8 times more CO2 than the CO2 produced by the pump over the course of a year. Of course that is still a good result, but because greywater heat recovery systems don’t require a pump, all energy collected (in the form of warming the incoming water) is counted. Hence its better SAP score.


Power showers

(From an original blog posted on a year of showering variously)

Over 30 years ago I plumbed in my first power shower – thankfully not the first of many. It was over a freestanding original Victorian cast iron bath (complete with lion’s feet) in the middle of a bathroom that was as big as my sitting room. It was the most powerful shower pump on the market at that time (at 3 bar) and, combined with a nine inch shower rose was sized to deliver 20 litres of water a minute. It was a thing to behold – especially given the showers I was used to installing back then.

Installation completed I turned on the shower to check that everything was working perfectly. For about three minutes, whilst checking for leaks I marvelled at the stream of water emitting from the shower head noting that the noise of the water drowned out the noise of the pump. And then… nothing. No water at all! As it was obviously an electrical fault or catastrophic pump failure, I called over the electrician who fiddled around for about 45 minutes before declaring that he couldn’t find anything wrong. In the words of Right said Fred, “We were getting nowhere. So Charlie and me ‘ad another cup of tea and then we went ‘ome…”

The next day it was working perfectly again for another three minutes… Eventually we realised that the fault wasn’t with the pump at all. The dry-run protection mechanism was cutting in because the mains could not refill the cold water storage and feed cistern (or “tank in the loft” as the non-plumbers amongst you may call it) fast enough, so it was being completely drained. And the moral of the story? Well, you would hope that it would have been to get a smaller pump, but of course it wasn’t. It was to upgrade the mains, and increase the size of the storage cistern to 150 gallons (670 litres) capacity! (Unvented cylinders weren’t an option then)

Nowadays a shower pump at 3 bar is quite tame (see size doesn’t matter) and 30 litres/minute is easily achievable (combined with a specially designed shower tray to ensure the bathroom floor doesn’t flood!).

So what does a shower of 30 litres/minute mean across a whole year? Assuming a 5 minute shower (calculated by the Government as the UK average) then it would require 150 litres of water compared to 35 litres under a shower like mine. Over the course of a year, showering every day, would result in an extra 41,975 litres of water. In a more alarming, but quite likely scenario of a 10 minute shower a day (after all, why upgrade to such a high spec shower unless you felt that it is all about the showering experience rather than just getting clean), the extra water required for just one person’s shower, becomes 83,950 litres.

That amount of water would provide all the water requirements for a year for 1.5 ‘average water users’. Or, 3.3 Caths (the new unit of measurement in the water field; like ‘the size of Wales’ only more egotistical).


Plumbing for architects

I think combis are only for small installations? Is this correct and how big a dwelling, and how many bathrooms?

Most combi boilers are recommended for dwellings with one bathroom only, due to the low flow rates of hot water they supply. Combis are rated on a certain number of litres (usually 10-15) a minute of hot water supply at a temperature rise of 30 ° C. However there are large combi boilers now available on the UK market. For example the Greenstar-highflow-550cdi (a floor standing combi boiler from Worcester Bosch) provides 25 litres/minute at a 30 ° C rise, which is suitable for two bathroom properties.


Public Toilet Design

‘Britain exported gender inequality and toilet queues to the rest of the world.’ This great quote by Michelle Barkley (toilet expert and architect) is perfectly summed up by this floor plan for public toilets in London in the early 1900’s. (Apologies for the poor quality but thought worth including – a picture is indeed worth a thousand words, most of them rather rude ones!)

toilet 1

On the same theme, Clara Greed blogs about how gender inequality in toilet provision is the missing link in creating sustainable, accessible and equitable cities. Read her blog here.

And if you are designing public toilets please don’t fall into the trap that equal size is equal toilet provision.

toilet 2

Barrier MDPE

If you are laying (or more likely specifying) a new mains supply to an existing or new build property you run the supply in blue MDPE pipe. Simples surely? Well not in all cases. Because if the building is within 40m of a railway line then apparently other rules apply. And this seems to be any part of the building even if it’s the rear and the mains supply is going in at the front. In such cases you are required to lay blue MDPE barrier pipe, which has an inner core layer of aluminium sandwiched between two layers of MDPE, and is identified by black/brown stripes along its length.

There are certain types of contaminants in the soil that can degrade standard MDPE pipe. WRAS’s Water Regulations Guide to the 1999 Water Regulations states that: ‘every water fitting shall be of an appropriate quality and standard and be suitable for the circumstances in which it is used’ and, more explicitly, that: ‘water fittings made of plastics or other material which are likely to be damaged to exposure by oil, petrol or any other contaminant, should not be laid in contaminated ground or should be protected’. (Guidance G4.16)

Hydrocarbons such as oil and petrol are the biggest risk, but a whole range of different manufacturing or industrial sites could cause problems. Affinity Water’s website states: ‘in the absence of a ground condition assessment for a new or replacement supply, where the site is currently used as or has previously had activity in one of the above categories, we are very likely to ask you to lay your supply pipe in an approved barrier pipe material.’ The categories they list include old chemical works, garages, petrol stations, gas works, landfill sites, scrap yards and railway yards, but being within 40m of a railway line is not mentioned. If you are building on contaminated land it is likely that you would be au fait with all the different regulations around building on such sites. But merely replacing an old lead mains into a dwelling on a residential street?

It might be that the water companies have only just started to interpret the regulations in this way because, not having heard about this before, I came across two examples in the last week, both in London. Both had installed standard MDPE pipe as unaware of the requirement and are now faced with the bill of digging it up and replacing with barrier pipe or the water company will disconnect the supply.


Managing Water Use in Scarce Environments

I bumped into Martin Shouler from ARUP a while back and he asked me to link to this excellent report  by the 2030 Water Resources Group. I had already done so in the ech2o newsletter this time last year, but this blog reaches a different audience and the report is really interesting. The Group has calculated that by 2030 the gap between safe freshwater demand and supply will be about 40% globally if the current approaches to water management continue. Such a scenario obviously has grave environmental, economic, social and political implications. Managing water use in scarce environments is a series of case studies from around the world looking at exemplary use of water at the agricultural, industrial and municipal levels. Projects are chosen that demonstrate a positive impact in a basin specific context and the difference is highlighted between consumptive use and non-consumptive use. I thoroughly recommend it

Posted on the AECB website January 2015

AECB Water blog 5