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Mar 02

Data explored

Thanks for all the responses to our post about data - it’s great to know there’s so much interest and enthusiasm for passivhaus out there. As always, the blog was deliberately as non-technical as possible and it was clear that a variety of assumptions have been made, but some readers have asked me to elaborate a little on it, specifically about the provenance of the data and the assumptions made. So here goes…

The data is collected from the following meters:

• The electricity meter for electricity;
• The gas meter for gas;
• The PV generation meter for PV; and
• The control panel on the solar thermal system for solar thermal.

We also now have a sub-meter on the MVHR, installed in September 2011. On 27 Feb, the MVHR sub-meter showed 1,259kWh. Please note that the MVHR is a Genvex Combi 185 which does three things: provides mechanical ventilation, has a heat pump that produces hot water when the solar thermal is not doing so and provides any space heating required, also through the heat pump.

Turning to that MVHR sub-meter, we can address the assumption made about proportion of electricity used for ventilation, heating and hot water. In my post I assumed 50% consumption by the MVHR. This was based on two things:

1. The sub-meter figure for the six month period, Sept 2011 to Feb 2012 inclusive, was 1,259kWh. 4 of these months sit within the year’s data period, but for the sake of painting the full picture, we extrapolated the 6 month figure to 12 months by doubling it and then applied it back to the whole of 2011 - i.e. 2,518kWh. Clearly, this is not perfect, but given that this 6 month period  covers the coldest months and therefore the months when the MVHR would actually be consuming the most energy, I figured it would be fair; if anything it assumes too high a consumption by the MVHR.
2. As a control on this number, I compared the balance - 2,549kWh - (i.e. energy used for lighting and aplliances) against average energy used in this way in the UK. There is a wide variation in estimates for this number, but somewhere around the 3,500-4,000kWh number is reasonable. 80% of our lighting is low energy and we are generally careful not to waste electricity, so it’s reasonable to work on the basis that our consumption will be lower than the average. That said, we still use an electric oven, microwave, fridge, kettle, TV, washing machine, dishwasher etc etc, so it’s likely that our consumption will not be cut by more than 20-30% - i.e. down to about 2,600kWh. And there is plenty of data to show that a young family, at home for most of the day has considerably higher consumption than average. So this seems to be a reasonable cross-check to support the assumption above about the MVHR.

From a passivhaus point of view, there is a bigger question here - what percentage of the energy is used to drive the fans and for heating water and what percentage is used for space heating? Unfortunately we don’t have metered data to show the relative percentages for each component of the MVHR and so have to make assumptions about how it breaks down. The assumptions are as follows: 

• Fan energy consumption is 964kWh per annum (110w power consumption, running 24 hours a day, 365 days a year)
• Hot water delivered energy consumption is 531kWh (assumptions are COP of 2, 5% standing losses, 55% solar fraction)
• Leaving space heating as the balance - 2500kWh less (964kWh + 531kWh) = 1,005kWh for space heating. Multiply this by a 2.5 COP of the heat pump to give 2,513kWh for space heating. Divide this by the treated floor area of 195m2 to give 12.88kWh/m2/annum.

Someone pointed out that I shouldn’t have gone to a decimal place (i.e. 12.8kWh per m2) given the assumptions made. Fair enough, let’s call it 13kWh. This still shows PHPP in a pretty good light and is testament to the skill and attention of the builder in delivering the design.

Finally, why did I assume 50% of the PV was consumed onsite? Two reasons:

1. That is the assumption for feed-in tariff export and has sort of crystallised in my mind.
2. It struck me as reasonable based on my (frankly obsessive) observations of the system output and OWL monitor during the peak solar pv months last year (May, June, July, August, September).

But it’s true, it could be wrong…so let’s assume 100% of the electricity is used onsite (which is DEFINITELY wrong) and see what a difference that would make. It would take electricity consumption to 5,480kWh, but have no effect on the space heating kWh/m2/annum figure, which is taken from the space heating figure.

Of course, we would much prefer to have perfectly measured data for all of this and  we will soon have better-but-not-perfect data, but in the meantime it would be a shame not to share and explain what we do have. In this case, we can’t do this without making some assumptions and  are more than happy to explore these further with anyone interested.

Feb 29

Anonymous asked: I have got one of those "draughty, freezing, solid brick walled Victorian houses" so am really interested. The BIG question - what did it cost to do the retrofit?

Hi,

Either I am really stupid, or tumblr really doesn’t show the date when a message was sent. So, if it has taken me ages to reply to your message, then apologies.

To answer your question, if you are doing a major renovation, you should add about 25% to the total cost for energy-related measures. If you are not doing work anyway, then this turns into 100% and then it depends on all sorts of things like size of house, finish/spec etc.

The key question is how deep a retrofit would you be interested in doing? You don’t need to retrofit to passivhaus to considerably improve the comfort in your home and reduce your bills.

If you would like to find out more about some of the less extreme projects we have worked on, feel free to drop us a line on info@greentomatoenergy.com.

Tom

Feb 22

A year’s data…da-dah!

Sorry for the long, long gap since my last post - we’ve been busy applying what we learnt on this project to many others around the UK.

We finally have a year’s worth of data, represented (rather boringly, sorry) in the graph below:

A bit of background about the electricity consumption number:

• it includes all electricity used onsite - i.e. MVHR fans, air source heat pump for heating and hot water when needed and lighting and appliances etc.
• we now have a meter on the MVHR, so will be able to attribute proportion of consumption to that (i.e. ventilation, non-renewable heating and hot water) later this year once we have a full 12 months’ data.
• it assumes 50% of the PV system’s energy was consumed onsite.

The gas is for cooking only.

If we assume that half of the electricity consumed was for lighting and appliances, then the other half was for fans, heating and hot water via the MVHR. Over the 195m2 of (“treated”) floor area, this 2,500 kWh consumption equates to 12.8kWh per m2 per year - this is exactly the same number that we predicted in our PHPP model. Amazing!

Nov 16

International passivhaus open days

Last Friday and Saturday we opened up the house for International PassivHaus open days. (Seems funny writing that - who woulda thought that’s something we would be end up being involved in.) Anyway, we are proud members of the passivhaus community so it was a pleasure to share the love.

I would write all about our wonderful tours, but luckily one of our visitors has kindly saved me the trouble -

http://londonecohouse.com/blog/uks-passivhaus-retrofit/

Couldn’t have put it better myself!

Jul 28

Chris Huhne pops in!

The Minister for Energy and Climate Change - Chris Huhne - visited the house this morning. With the Green Deal launching next year, the tour was part of the Minister’s ongoing fact-finding into low energy housing.

He seemed to be impressed by the technical work we have done, as well as the finished product. However, quite understandably, his main concern was in respect of the scalability of a project of this complexity.

The UK needs to significantly reduce the energy consumption of its existing stock if we are to meet our carbon targets and reduce dependence on imported heating fuel. In our view, “deep retrofit” of much of the housing stock - like what we have done here - must happen in order to meet these objectives. Anything less will mean either missing our targets and/or just re-visiting the same properties in the future, which is expensive and doubly-disruptive.

Even after this morning’s visit, we are still worried about the degree of standardisation proposed in the Green Deal and are still trying to work out how it will deliver the level of investment required to make these deep retrofits happen.

Photo, left to right: Edward Borgstein, Akta Raja, Chris Huhne, Tom Pakenham

Jun 01

[video]

Some data

So, we’re starting to get some data from the house. Admittedly, we don’t have the most advanced monitoring systems - i.e. me with a pencil (apart from the MVHR temperature data, which is quite snazzy, of which more to follow in another post) - but think we’re capturing the key data.

The electricity and gas readings are shown from 23 January 2011 - by which time the MVHR, solar thermal and solar pv had all been commissioned properly - up to today’s date. Both of the solar readings are totals generated since date of comissioning.

1. Gas consumption - 5.8 HCF, or 180 kWh (@31 kWh per HCF) - note, this is just for cooking
2. Electricity consumption - 1,837 kWh or 14.35 kWh per day (over 128 days)
3. Solar PV output - 330kWh (since 9th January 2011)
4. Solar thermal output - 1,198 kWh (since 16th November 2010) - total hours of operation (i.e. pump running) is 845 hours. Therefore, the 7m2 of solar thermal is putting out an average of 1.41 kW

The electricity consumption looks high, making me wonder about the extent of our parasitic load and actual power consumption of the MVHR. Theoretically, the MVHR should only use a maximum of 140w for its two fans and there will have been some consumption when the heat pump was heating the hot water, but we need to install a reader to confirm this.

It is instructive to look at the net daily electricity consumption (i.e. incorporating input from solar pv) by month, below:

• February - 20.46 kWh
• March - 14.51 kWh
• April - 10.1 kWh
• May - 8.96 kWh

We will put up some key data from the MVHR datalog soon. Most notable trend so far is impressive stability of internal air temperature.

Apr 05

My how you’ve grown!

Barely 1 month old and the roof meadow is already starting to flourish.

Mar 13

[video]

Mar 01

We did it!!!

The house has been officially certified as a passivhaus, hooray!

It has not been easy, but today we were presented with our passivhaus certification by the Godfather of the movement, Wolfgang Feist.

Now to get on with the important business of delivering low energy building in the UK.