Some important numbers

25kWh/m2, 40kWh/m2, 2,989kWh. Everyone reading this blog will probably recognise the first two, which are maximum space heating requirements for EnerPHit and AECB Silver Standard respectively. But the third figure? Well that is the amount of kWh required a year for the hot water of many an adolescent showerer. (30 minutes in a shower, once a day, or 15 minutes twice a day, with a flow rate of 7 litres/minute). Unpicking this a bit further we can see that a 100m2 dwelling retrofitted (or built) to the two standards comes in at 2,500 kWh and 4,000kWh respectively a year for the space heating. So our one adolescent requires more energy and is producing more CO2emissions than the space heating in a super-deep retrofit (and two thirds of a deep retrofit). This is why the measurement of hot water in post occupancy evaluations is so important! And why Passivhaus design in the UK needs to look at hot water use more closely.

The fuel cell – has its time arrived?

Well, I think it finally might have! Fuel cell technology to produce electricity as well as heat in homes seems to have been just around the corner for ever – I first heard it being touted as the next big thing in 1998 – but the industry has met with little success, with systems stuck at either the laboratory or field test stage for years.

Fuel cells as part of a CHP (Combined Heat and Power) system use hydrogen and oxygen which, when mixed in the right quantities, react chemically to produce electricity and water. The hydrogen comes from natural gas (CH4) and the oxygen from a balanced flue air intake. The process produces waste heat at 62OC which is used for space heating and hot water. Viessmann have recently brought the Vitovalor 300-P (a micro CHP unit using fuel cell technology to generate the electricity) onto the UK market. The system comprises a fuel cell module and the “peak load” module (basically a hot water cylinder and the back-up boiler) and was displayed at this year’s Ecobuild. Along with other boiler companies they have been working on fuel cell technology since the late 1990’s but in a move from the norm have teamed up with Panasonic to design a boiler that shows your favourite TV programmes when running in ‘eco’ mode…. (I jest of course).

What Viessmann have done is combine a Panasonic fuel cell that uses PEM (Polymer Electrolyte Membranes) technology with their boiler and controls in a single package. PEM fuel cells are well established in Japan where there are 20,000 installed appliances. The fuel cell has to be adapted for the European market as the gas supplied in Europe is not as clean as that in Japan; this is achieved by fitting different filters into the fuel cell. So, proven technology (20,000 working fuel cell units behind the first one installed in the UK, instead of just a few factory and field test models) combined with the heating and controls expertise of Viessmann. Sounds like a good match.

The system costs £20,000, which means it will be limited to the few early adopters who can afford that kind of money. It is eligible for a Feed-in Tariff of 13.45p (at the time of writing) available for ten years, but the large upfront cost is certainly a barrier, especially as average yearly generating figures of 4,500 kWh a year over 10 years is a return of just over £6,050 from the FiT. Viessmann would like to see upfront costs being met by grants (or interest free loans partly paid back via the FiT) as the best way for numbers in the UK to reach critical mass.

Some numbers from Viessmann. The Vitovalor 300-P requires 2.5 kW of gas to run and produces 0.75 kW of electricity while doing so. Currently it is twice as efficient as importing electricity from the grid. During the winter months it runs 20 hours a day and in the summer months about 4 hours a day. The unit delivers 4,500kWh of electricity a year on a run time of 6,000 hours. (About the same as a 5.3 kWpeak PV array). On a yearly run time of 6,000 hours it requires 15,000kWh of gas. To make the carbon and savings and costs stack up you want it to provide no more then 25,000kWh of heat and hot water a year. (Any shortfall in the requirement for heating is met by the gas condensing boiler which is part of the unit). The unit is suitable for a detached house (maximum heat output is 19kW) but it does not make economic sense if more than 25,000kWh of space and water heating is required a year so the thermal envelope on an existing property will require upgrading. (Though obviously anyone reading this blog wouldn’t even consider anything else!)

It requires a return temperature from the thermal store of less than 40OC to ensure the chemical process continues; if the temperature exceeds 42OC in the unit itself it cuts out automatically. Therefore it is best combined with underfloor heating (though it is possible to use low temperature radiators and/or weather compensation). In winter the temperature of the return is managed by dumping the heat into the heating systems. In the summer months that cannot be done (hence the run time of 6,000 hours out of a total 8,760 hours in a year). If you want to know more, here is the link to their website.

There are a couple of other points to make. The stack (which is basically the gubbins of the fuel cell) has a run time of 70-80,000 hours so will need to be replaced in 12-15 years. Current price for that is 2,000 Euros. And, as with all CHP technology it does not make economic sense to combine it with solar thermal.

Should it replace the condensing boiler? Or is this just another example of green bling and shouldn’t we still be looking at centralised supply systems? Maybe, but I like what I have seen so far…


The mysterious case of the misspecification of electric showers

85% of UK households have a shower (if you include showers connected to bath taps.) and 52% of all showers sold in the UK are electric showers. Though that does not mean that 52% of showers are electric, there are an awful lot of them in UK homes. There are lots of things I don’t like about electric showers; their puny flow rate, their high carbon emissions for that self-same puny flow rate; the fact you can’t turn them off while you soap up and then turn them back on again without getting scalded; their inherent ugliness (a box on the wall in the bathroom basically). But what I dislike most about them is the fact that they are bought by unsuspecting consumers or specified by architects, both of whom appear to be labouring under the same misconception. Which is that electric showers are easy to fit / will outperform the current shower (in a scenario of a shower fed from a Cold Water Storage and Feed Cistern / are the only choice in a loft conversion.

Instead of ‘puny flow rate’ maybe I should say ‘water efficient’, as since electric showers heat the water instantaneously their flow rate is limited. The first electric showers available in the UK (back in 1972) had a 5 kW heater, and the maximum flow rate at any significant heat was less than 3 litres/minute. Now the most powerful electric showers are rated at 10.8kW and provide a flow rate of 4.9 litres/minute at 40OC, increasing to 5.9 litres/minute if you are happy with a lukewarm shower. In an attempt to increase the satisfaction factor of electric shower users, a lot of thought goes into the branding of electric showers.

The Mira Sport – wow!
The Mira Sport Max – double wow!!
The Mira Sport Max Airboost – triple wow!!!

So why are they not simple to retrofit?

An electric shower needs to connect to the mains water supply and (obviously) requires electricity to work. The mains water supply is usually easy as, in most dwellings where these showers are installed, there will be a mains supply up into the loft to feed the CWSC and it is a simple matter to tap into it. But the electricity supply? You cannot (despite what many people assume) connect an electric shower to the lighting circuit. Nor even to the power circuit feeding the sockets. The I.E.E. Regulations require a dedicated supply from the consumer unit in 10mm2 cable protected by a 45 amp fuse. And, 10mm2 supplementary earth bonding from the shower to the shower tray or bath. Not so simple to fit now is it? The same regulations will also not permit your rather crappy shower to be upgraded to the new Airboost Max (or whatever) just by changing the box, because the cable size to the existing shower will be 4 or 6mm2. So it’s not even easy to fit when you already have an electric shower.

water blog 1So what should you buy/specify?

Electricity in the UK is very carbon intensive. 0.54 kgCO2 are produced for every kWh of electricity supplied compared to 0.19 kgCO2 from gas. So, if your hot water is already heated by gas, it is better to install a thermostatically controlled shower fed from the hot water supply. If you have a combi boiler the pressure will be 1 bar plus and the shower will feel great, even at a regulated flow of 8 litres/minute. If you have a hot water cylinder fed from a cistern in the loft, the pressure will be 0.2 bar if the bathroom is on the top floor and the shower won’t feel so great. Its flow rate will also be lower, probably only reaching 5-6 litres/minute, but, in my opinion, it will still feel better than an electric shower

This is a shorter version of June 2014’s a year of showering variously blog. It is also far politer about architects!

Arbed dŵr

I have been doing a lot of this in Wales recently – saving water for the non-Welsh speakers reading this blog – as part of designing and delivering several water efficiency training modules in partnership with the Centre for Alternative Technology (CAT). As such I have been updating my knowledge of the Water Framework Directive (WDF) so thought I would share a bit with you. A European piece of legislation, it came into force in December 2000 and became part of UK law in 2003. Its purpose is to enhance the status of, and prevent further deterioration in, the ecology of aquatic ecosystems and their associated wetlands and groundwater. It commits all European Union member states to achieve ‘good’ qualitative and quantitative status of ALL water bodies (including marine waters up to one nautical mile from shore) by 2015. The WFD requires that inland and coastal waters reach good chemical and ecological status or potential as set out in River Basin Management Plans (RBMPs). The WFD also promotes the sustainable use of water and sets out to ensure abstraction rates are at a sustainable level.

Water bodies are classified as bad, poor, moderate, or good ecological status and assessed according to the following criteria:

  • biological quality (fish, benthic invertebrates, aquatic flora)
  • hydromorphological quality such as river bank structure, river continuity or substrate of the river bed
  • physical-chemical quality such as temperature, oxygenation and nutrient conditions
  • chemical quality that refers to environmental quality standards for river basin specific pollutants.

In 2012 Natural Resource Wales (NRW) reported that only 37% of the water bodies in Wales had ‘good’ ecological status. This figure increased to 42% in 2014. And by 2015 NRW expects 50% of the water bodies in Wales to have ‘good ecological status’. Whilst this is far from meeting the terms of the WFD it is better than England, where, in 2015 just 17% of England’s rivers are judged to be in good health, according to Environment Agency figures. (Down from 29% in 2014, although the Environment Agency says the figures look bad because the EU’s assessment criteria have been tightened).

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The Propelair toilet

I first came across the Propelair toilet in approximately 2009 when it was being trialled at WRc basically to check whether the small amount of water used to flush (1.5 litres) would cause any issue in drain lines with relation to drain carry of poo and toilet paper. All trials proved that it didn’t. Of course drain carry was shorter. But basically the poo and loo paper continued its journey into the sewers in a series of short hops; a head of water would build up behind the stalled poo and once it overcame the frictional resistance would move it along again. (And this was not relying on bath water, just more WC flushing). It took another few years before it was launched on the market and in that time the design was improved, though the basic flushing principle remains the same. The Propelair has a two section cistern. One side has a water reservoir and the other side has an air pump. When the toilet is flushed 0.5 litres of water enters the pan to wash the sides down and then the air pump is activated. The pump ‘displaces the air’ (using ‘patented air displacement technology’). Basically it forces a jet of air into the pan which pushes the contents of the pan down the trap (with a satisfyingly loud whooshing sound!). The remaining 1 litre of water flows into the pan to refill the trap.

When a standard toilet is flushed airborne water droplets are produced. Because the seat has to be closed to flush the Propelair, the issue of contaminated water droplets being expelled into the air is prevented.

The pump does require electricity to run but uses very little – 1000 joules per flush, meaning 1000 flushes for 1kWh of electricity. 1000 flushes would save you 3000 litres of water. (Worked out at 3 litres saving per flush, from a 4.5 litre single flush – as will be mostly in public toilets – down to the 1.5 for the Propelair.) 3000 litres of water is 3m3. On average it takes 1.2 kWh of electricity to supply 1m3 of treated water into the UK’s buildings and take the same amount away to clean it. . So the overall saving on electricity will be 2.6 kWh for every 1000 flushes, an excellent result (through there is no information on how much power any standby mechanism pulls).

When I first saw it I was impressed because it was using so little water. Now, having used one several times I am impressed by the fact it clears the pan so reliably. (This is after many years of poorly performing WCs, when, after flushing, you are left gazing forlornly as the remaining contents bob around in the pan.) Maintenance will be required of course, but then maintenance is necessary for all WCs. I will be interested to see if there are any reliability problems. I hope not because I think it is great.

Posted on the AECB website June 2015

AECB Water blog 6