“This Victorian Mid-terraced refurbishment to passivhaus standard was the standout entry in this category. The project shows what can be achieved in the refurbishment of homes, which will be increasingly important as we look to upgrade our housing stock.”
We have just had our second summer The good news is that, with a little bit of occupant management, both summers have been a great success – the house has stayed cool and fresh, with minor instances of localised over-heating.
When we modelled the property in PHPP, the possibility of it overheating was highlighted by the software. The PHPP model of the building estimated that there will be overheating 2.5% of the time throughout the whole year, this is when the internal temperature is above 25°C, so we were interested to see how it would perform against the prediction.
Data from the MVHR control unit, which is located in the living room, the hottest room in the house show that the room has been over 25°C for 7.1% of the year so far, this shows higher overheating than PHPP suggested.
However, CIBSE defines over heating as 26°C and above in bedrooms and 28°C and above in living spaces, the criteria for an overheated building is when > 1% of annual occupied hours are at these temperatures. Due to enormous pile of data we would have to wade through to assess a whole year, we have looked at the data from May until the end of August 2012. It shows that the living room was 28°C and above for 4.3 hours during this period, all of these hours being on the same day when the maximum external temperature was 30°C. This gives the percentage of overheating defined by CIBSE, to be 0.11% for the year so far. This is nearly 10 times lower than what would be classified as an overheated building.
Occupants report that whilst the house can get hot on very hot days - like any other house - it is quick to cool down and the temperature can be quickly and effectively managed by simply opening windows.
It is worth explaining and exploring some features of the property pertinent to its summer heating profile:
South facing – the house faces more or less due south. There is a lot of glazing on the south façade, 53.7% to be precise. As a result, a great deal of direct solar radiation enters through the front of the building, causing rooms on the south side of the building to be noticeably warmer than those on the rear / north side.
Thermal mass – due to the wall build-ups and structural (read “budgetary”) constraints, it was not possible to include any thermal mass in the rooms on the south side, at any level of the 4-storey building. The kitchen at the rear of the building has a concrete floor, which appears to contribute to keeping that area cool, but does not provide any thermal mass to the hotter, south-facing rooms. We explored more affordable / lightweight options, but thermal mass plasterboard and clayboards were not easily available when we built the property.
Underfloor heat exchange – there is a ground-to-air heat exchange under the floor in the cellar. It is there to pre-heat incoming air before it reaches the MVHR in the winter; and pre-cool it in the summer. The air is taken in from the north side of the property, so that in its self means the air will be cooler in the summer than if taken from the south. Unfortunately, we do not have sophisticated enough monitoring in place to record its effectiveness from a cooling perspective. Similarly, because the windows are often open to provide passive ventilation (in addition to the MVHR), it is hard to know whether this element contributes anything meaningful to the internal temperature.
External shading - because the house is in a conservation area, it was not possible to add any external shading without planning permission. So before going down that route we decided to see how hot the house became and tackle this issue in future, if necessary. Whilst it’s true that external shading would increase comfort in the house, overheating is nothing like a big enough problem to warrant all the effort and cost involved in adding external shading. It’s always an option in future if the climate continues to get hotter…hmmm.
Passive ventilation – The main temperature control technique in the house is good old-fashioned passive ventilation; i.e. opening some windows. Because the house is tall and the ground floor generally stays so nice and cool in the summer (particularly with the north-facing kitchen door open), we generate an excellent stack effect bringing cool air up through the house and expelling hot air through the velux windows on the top floor. This generally means leaving one small bathroom window open (on tilt, so secure) most of the time when we’re in and one window at the top of the house open. If it’s very hot, we will open more windows to increase the flow of air. It is an exceptionally effective way of keeping the house cool and makes one wonder why anyone ever uses air-conditioning (in most scenarios).
For rapid cooling of particular areas that are “off the stack”, we also occasionally use cross-ventilation, but this is less desireable because of the presence of a reasonably busy road on one side of the house.
Some people ask why we don’t just turn the MVHR off in the summer seeing as we have windows open. The answer to this is twofold:
We don’t open all the windows, particularly not at the front of the house which is on a relatively busy road. Therefore, some continued ventilation is required from the MVHR in these areas;
Unless it’s extremely hot, we tend to close the windows at night and it would make sense to keep turning the MVHR on and off; particularly if doing so risked forgetting to turn it on again at night!
All-in-all, whilst it is during the winter that the house really comes into its own, the good news is that it is a comfortable place to be even on those rare hot summer days.
Whole house energy costs of less than £200 per year!
Exciting news - the energy cost for the house has come in at less than £200 for the year 2011-2012; £189.40 to be precise.
The excellent people at Good Energy have provided me with a breakdown of all of our bills (gas and electricity) and credits (e.g. Feed-in Tariff and HotROCs) for the last year.
It looks like this for each element:
The gas is just there for cooking and more than half of it is for the standing charge. Every time I see this it makes me regret not installing an induction hob…
Avid readers of this blog (of which there are many millions) will know that we don’t yet have a year’s worth of data on the MVHR sub-meter. This means that we can’t split out (a) electricity used for ventilation, heating and hot water from (b) electricity used for lighting and appliances.
For those who are not familiar with HotROCs, they are a rather pleasing initiative offered by Good Energy for people with solar thermal systems who are still not receiving the RHI (which was “promised” by various governments, ministers etc, but is still not being paid and may well never be). Apparently Good Energy is reviewing this offer, so let’s hope they don’t decide to pull the plug.
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:
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.
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:
That is the assumption for feed-in tariff export and has sort of crystallised in my mind.
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.
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?
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 firstname.lastname@example.org.
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!
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 -
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.
Gas consumption - 5.8 HCF, or 180 kWh (@31 kWh per HCF) - note, this is just for cooking
Electricity consumption - 1,837 kWh or 14.35 kWh per day (over 128 days)
Solar PV output - 330kWh (since 9th January 2011)
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.
This week we dipped into the world of “eco-paints” in an attempt to find the best solution for our house. It is not an easy process. There are lots of brands making lots of claims that fall under the broad category of “eco-friendly”, but without doing a Phd on the subject, it is incredibly difficult to compare. Sorry that this post is so long, but hopefully it will be interesting/helpful.
The main reason seems to be what counts as being “eco”. Some paints, eg Earthborn, concentrate on the impact of their paints on the living environment of the user compared to traditional paints. The argument here is that conventional paints can release harmful chemicals into the air, whereas Earthborn’s “natural” paints are water based and contain no VOCs* (the real bad boy in paint) or acrylic softeners.
However, even if these claims are sound (I say this because there is sporadic debate about whether the alternative ingredients of “natural” paints also have a harmful effect on health and the environment), they don’t drill down into other considerations such as the carbon emissions of the manufacturing process.
Also, on another point, without buying and testing a million different pots of paint from each brand (which wouldn’t exactly be eco-friendly), it is impossible to get a thorough comparison of how the different brands compare with one another in terms of opacity and durability. Clearly, even if a paint scores highest in terms of eco-friendliness on a litre by litre basis, if you need to buy a whole lot more litres to do the job, or if the paint lasts only the half the time of one of the competitor brands and needs to be replaced, its high score gets chipped away.
So, somewhat reluctantly, we accepted that without being able to compare reliably, we were not going to find a clear winner. Instead, we decided to go for a brand which appeared to tick as many boxes as possible.
Our choice is Dulux’s Ecosure range. This feels like a cop out but that may just be because of inherent doubts around big mainstream providers jumping on the green bandwagon with token offerings and lots of greenwash… However, putting our natural scepticism to one side, we think that the Ecosure range fares pretty well against out key criteria:
Almost zero VOCs. According to Dulux “no organic materials such as solvents are added in the manufacture but some of the raw materials that are used can contain traces of volatile components which is why this figure can never really be absolutely zero.”
35% less embodied carbon. This was based on analysis of the lifecycle of the new range, developed in conjunction with the sustainability charity Forum For The Future, compared with the standard Dulux Trade range, from extraction, growing and re-processing of raw materials to the manufacturing process itself. What we couldn’t find were the actual figures showing what the embodied carbon was reduced to or from.
Packaging contains 25% recycled plastic
“High opacity provides excellent coverage and application” (we couldn’t test this claim, but Dulux produces some charts showing high performance compared with unnamed “eco brands”. Presumably we will find out as we start to use it…
The Ecosure range is more expensive than standard Dulux paint, but probably broadly comparable to other eco brands, although it is difficult to assess as you need to take into account average coverage of the paint as well as the cost per litre. For comparison, the Ecosure is approximately £10 more expensive per 5 litre pot than standard Dulux matt emulsion.
The easiest sell for Dulux is the beautiful colour charts they have. “Greenness” is all very well, but other colours are very important too! Unfortunately, none of the other eco brands that we were looking at could offer us a showroom at the end of our road with a library of beautiful colours and a stool to rest a weary pregnant body on…. I fear this may be the main reason we ended up with Dulux, but please don’t judge me.
It is a bit unfair to judge Dulux above other green brands on this element, as some of the other brands we came across said that they would match any colour, but in terms of ease and practicality, this where mainstream providers do come into their own.
Some more options
In order to give a bit of balance, there were a few brands we came across that looked great, responded promptly to our queries, and appear to offer a good spread of colours. If we had the time and tools to do a proper comparison of their products against the Ecosure range, we suspect they might have done rather well:
Paint The Town Green – who manufacture their paint in a “green” factory in Iceland which uses hydro-electric and geo- thermal power.
Auro paints – whose ingredients are sourced as locally and ethically as possible and whose factory uses wind power and solar energy to help with energy supplies and rain-harvested water for washing down machinery.
Anyway, enough talking, we need to get on slapping some paint on the walls asap if we’re going to get into this house any time soon.
*NB it should be pointed out that there is new legislation in effect which means that from 1 January 2011, VOCs levels in paint will be subject to certain restrictions depending on the particular use to which the paint is being put. There is more information here.
To those people who have been reading this blog, apologies for the long delay since our last post. The reason is that the build (and a few other things) have quite simply overwhelmed us.
You’ll be pleased to hear that everything is back on track and we can bring you all up to date with the huge number of things that have changed, progress that has been made and obstacles that have been overcome.
First, a quick explanation of why and how the build has been so time-consuming to stop us squeezing even this most pleasurable of things – writing a blog – into our timetable:
IT’S SERIOUSLY DIFFICULT TURNING A VICTORIAN TERRACE INTO A PASSIVHAUS
Of course, any less ridiculous family would have realised this long ago, and ruled the project out accordingly. Had we accepted it, we may have done that too, which is why we chose to pretend it would be easy and press on regardless. The good news is that, after much financial wizadry (no, nothing dodgy) and perspiration, we’ve come through the nervous-breakdown stage and are now remarkably close to having a house to live in. Well, sort of – the last statement assumes that we:
1) successfully build 10 triple-glazed, sash-lookalike windows
2) Take delivery of two sets of triple glazed French doors from Latvia sometime before the middle of next year
3) Somehow carry a 250 kg unit the size of a tank down the stairs into our cellar;
4) Manage to integrate our solar thermal tank with our MVHR/heat pump/hot water combi unit
5) Build a passivhaus standard front door
6) Close off all remaining thermal bridges
7) Achieve 0.6 airtightness
8) Manage to penetrate the zinc roof with metal bolts for the solar PV system 20 times without ending up with a single leak; and, most challengingly of all,
9) Work out how the hell to build a house that doesn’t overheat in this scorching weather…
So, those are just a few of the things we will be writing about in the coming weeks, along with special features from guest writers on such fascinating topics as:
1) Paint – unravelling the puzzle of “eco paint”.
2) Embodied energy – so, what’s the final footprint and how quickly will it pay itself back?
3) Finishing – what wonderful things are there out there to create a beautiful house within an environmental framework?
4) Lighting – without the help of a rocket scientist, is it possible to light the house beautifully, affordably and within energy constraints?
5) Materials – what are some of the other environmental considerations (i.e. non-energy) that need to be borne in mind when selecting materials?
So, fasten your seatbelts everybody and get ready for some serious low energy retrofit excitement!
Taking place less than a mile away from our project site is this year’s Ecobuild exhibition - http://www.ecobuild.co.uk/. We took a break from our busy schedule of knocking walls down yesterday to have a look at the latest in green construction technologies.
It’s lucky that it goes on for 3 days - you’d need that long to visit only half of the stands and seminars at the exhibition. There was an excellent presentation on passivhaus principles by Paul Smyth from Inbuilt and on an almost-passivhaus retrofit by Andy Simmonds. His project is definitely worth a look - http://www.simmondsmills.com/project.php?id=31 - only falling down on achieving passivhaus certification through the airtightness test, our looming nemesis…
Other highlights were the huge living wall installation, the plethora of timber frame building providers and the installer programme.
If you are anywhere near West London and have a spare few hours (or days), you should definitely make a visit. And just in case you’re wondering, it’s free to get in.
After what seems like an age of planning, modelling and jumping through bureaucratic hoops, the works have finally started. The scaffolding is going up at a crazy speed - if I hadn’t seen it with my own eyes, I wouldn’t have believed that 20 stone men could clamber up the side of a building like hyperactive monkeys. Once the scaffolding has been erected, the first step is to build the loft. It will be super-insulated (finer details of build-ups and materials to be supplied at a later date), almost completely airtight and covered in solar panels, but otherwise just like a normal loft.