Summer 2013 - has the house kept its cool?

I have been asked this question throughout the summer. Last summer was so cold that we were not able to assess how well the building performs in hot weather.

Unfortunately, we don't have data loggers or similar equipment to provide lots of quantitative data. That said, July was our warmest month with temperatures in the high 20s (Centigrade) and from memory hitting 30C on one or two days. The house remained comfortable thoughout nearly all of that period within internal temperatures between 22C and 25C. We did have one day when the temperature in my home office (which has a PC with two monitors, one of which is quite old and gives off significant heat) reached 27.5C and it did feel a bit too warm. Other rooms in the house felt quite comfortable throughout.

Our cooling strategy

Site constraints meant that we needed more east and west glazing than one would have in an "ideal" Passivhaus. This meant needing to use external blinds or similar, not an overhang type shading device which is possible on a south facing window because the sun is lower in the sky in morning and evening. So....

1. We chose to fit Internorm windows with integral blinds - see below - this was a solution specific to our local circumstances, as the window is not a true triple glazed window, consisting of a sealed double glazed unit, and internal venetian blind and a third pane on the outside of the blind: 2 + 1. The blind is in a ventilated space. This means that they have a whole window U-value of only 0.93W/m2K, less than would be needed in many parts of the UK. Internorm do a 3 + 1 window, with a lower U-value but it is considerably more expensive, very heavy and they use Krypton, which is best avoided (more expensive/rare and - when it leaks out as it will after about a decade - results in a more greater drop in performance than Argon-filled units. All the windows on solar gain facades have high g-value glazing (60%), so they will capture 20% more heat than typical 50% g-value triple glazed units. This means that remembering to use the blinds is key to keeping the house cool. This can be solved by using automation but this seems like a step too far in complexity in a domestic situation; although perhaps it is a good idea in an office building.





2. We have to sliding pation doors, one on the east and on the west facade. These are "traditional" triple glazed. We planned two pegulas to provide seasonal shading on these two quite large glazed components. Unfortunately, we haven't got the pergulas in place yet, so we did get more solar gain than is ideal. I don't know how much impact this is having on the overall summer performance of the building. When I modelled it in the PHPP, it does affect the frequency of overheating and, had the pergulas been completed before this summer's not spell, we might have avoided the slight overheating on a day or two in July.
3. We do of course open our windows in the summer and I tried to keep the windows closed in the hot portions of the day (to help keep the heat out) and to make sure the windows were open at night. I think that if we were located in London (where night time temperatures don't drop as much), night time flushing would have been much less effective.

During the warm spell, I experimented with swiching off the MVHR at certain times of the day. Our intake (and exhaust) terminals are on the west facade wall. During the morning, when the west is in shade, I noticed that the MVHR seemed to help to maintain a lower temperature, as it was drawing in cooler air from outside. In the afternoon, it was drawing in warmer air and this possibly caused internal temperatures to warm more than might otherwise been the case. I tried switching off the MVHR in the afternoon but this seemed to make it feel less comfortable in the afternoon. I think that the reduced air change rate may have resulted in higher internal relative humidity levels, adding to thermal discomfort.

More generally, we have noticed that the house is more sensitive to internal heat loads than a typical UK home. Some of this is modelled in the PHPP but, in real world use, occupants may bring older electrical equipment, which will add to overheating risk. In my case, the old computer screen does give off significant heat and, although it is smaller than the newer one, uses more electricity. I don't think, however, that it makes economic or ecological sense to replace a perfectly good computer monitor.

Lessons learnt from this summer

1. Keep the MVHR running. Although it provides no cooling function (a common misconception amongst some Passivhaus sceptics), the regular air changes it delivers moderates internal relative humidity.
2. Use the blinds.
3. Consider the impact of internal gains - heat emitting devices will have a surprising impact.

Totnes Passivhaus at Ecobuild

Authors of the Passivhaus Handbook, Janet Cotterell and Adam Dadeby, will be speaking at Ecobuild on 5th March 2013.

Slot 1 – first 20 min presentation within 12.30 – 14:00 session – retrofit and new-build case studies – seminar room 1 – “Passivhaus – using Passivhaus to help obtain planning consent … ” see http://www.ecobuild.co.uk/seminars/session/passivhaus/91/tuesday-05-march/seminar-room-1.html

Slot 2 – last 20 min presentation within 15.45 – 17:00 session – “Totnes Passivhaus: exemplar retrofit to Certified Passivhaus standard” – seminar room 8 – “Self build and renovation” – see http://www.ecobuild.co.uk/seminars/session/sustainable-self-build-and-renovation/79/tuesday-05-march/seminar-room-8.html

The Passivhaus Handbook will also be for sale at the RIBA Bookshop stand - S1230 and S1330 in the South Hall of Excel.

The Passivhaus Handbook

The Passivhaus Handbook, A practical guide to constructing and retrofitting buildings for ultra-high energy performance is published tomorrow (25 October 2012). The book expands on the topics discussed in this blog.

The Passivhaus Handbook has been getting good reviews:

‘Passivhaus construction looks like becoming not just popular in the UK, but commonplace. This is a no-nonsense and engaging introduction on how to do it.’
Kevin McCloud, presenter of Channel 4′s Grand Designs

‘This book gives a wonderful overview of Passivhaus in the UK today, not only enabling interested parties to understand the principles and pitfalls for their own projects, but also for policy makers and planning officers to understand how to avoid some of their ‘own goals’ in attempting to encourage conservation.’
Peter Warm, Passivhaus Certifier, WARM Low Energy Building Practice

‘I have now recommended your book to our four individual current Passivhaus clients wanting to build a Passivhaus. Your book will save me hours and hours of having to explain the principles of what we are trying do, to first time clients on a steep PH learning curve.’
Andrew Yeats CEPH Architect, Eco Arc Architects

‘I’m delighted to see everything about Passivhaus and its application in the UK collated for the first tiime, in The Passivhaus Handbook. The first-hand experience of the authors provides an excellent grounding for the book.’
Jon Bootland, Chief Executive, Passivhaus Trust

Here is the description of the book from the Green Books website:

The Passivhaus Handbook is an essential guide for everyone wanting to realise a supremely comfortable, healthy and durable home with exceptionally low energy costs. Whether you are building an extension, retrofitting your house or starting from scratch; are new to low-energy design or already have some experience, this book will help you navigate around the potential pitfalls and misconceptions. It brings together current thinking and best practice.

Passivhaus design focuses first on getting the building fabric right, to achieve ultra-low energy consumption in the most cost-effective manner. The approach is relevant to a wide range of building types and climates, not just to special structures. Passivhaus methodology can be combined with elements of other building standards, such as the UK’s Code for Sustainable Homes, or with other goals, such as a commitment to use low-impact and natural building materials.

This book includes:

• A clear explanation of the underlying building physics.
• Detailed information on key elements: avoiding air leakiness, designing out thermal (cold) bridges, moisture management and ventilation strategy.
• Tips for creating a cooperative, motivated project team.
• Photographs and diagrams throughout.

With steeply rising energy prices, uncertain climatic changes and straitened economic times, the Passivhaus approach, proven over 20 years, offers a timely and practical response.

The Passivhaus Handbook is available from Passivhaus Store as well as from online retailers. I hope you find it useful.

We get our Passivhaus Certification

This week we had a little ceremony to mark getting our formal Passivhaus Certification. Rob Hopkins, of the Transition Network, kindly came to handover our newly gained certificate.
 

We have now been in the house just over two months and we are "looking forward" to a decent winter, to give the house a bit of a test. We are probably going to want to make some adjustments to our ventilation, once we have started using it to transport the small amounts of heat around the house. More on this in a future post.

From left to right: Janet Cotterell - Passivhaus architect, me - Passivhaus energy modelling (and client), Jonathan Williams - Passivhaus builder, Joe Bellows - one of the Passivhaus contractor team, Peter Warm - Passivhaus Certifier.

Living in a Passivhaus, the first few weeks

We have been living in the completed Passivhaus Home since 19 August and are really looking to seeing how the house will perform this winter. So far, the temperature internally has been pretty constant. The only time we had some overheating was over the weekend of 10th and 11th September, when we took part in the Open House event. We had over 150 people visiting and there were a lot of people in the house adding to the heat gain noticeably. It was warm, humid and windy outside (unusual weather) and we found that the tilt and turn windows, some of which we had tilted open to provide extra ventilation and cooling kept blowing closed in the wind.

We are still tweaking the settings on the MVHR unit (heat recovery ventilation unit). The MVHR is designed to recover the heat from the old, outgoing air and give it to the new, incoming air. Of course, during warmer summer weather, this is the last thing you want. So MVHR units are designed not to recover any heat when this is not needed.

The heat recovery was kicking in when it was not needed. We have tweaked the settings so that it only comes in at 18C (the minimum temperatures allowed) and turns off if the temperature reaches 20C. The picture above, which was taken a few minutes ago, shows that the summer bypass is enabled, which means that it isn't recovering heat - a bit counter intuitive.I must say that the user interface needs a little improvement. There's definitely a little product development work for Paul here. I feel that this is an often ignored part of a product's design. An impatient user might have decided just to switch the unit into standby until the weather got cold enough for the heat recovery to be needed, which would have defeated the purpose of the system. That said, once set up correctly, we shouldn't have to fiddle with this again.

Our hot water system has an even less user-friendly interface. Although this is not a Passivhaus specific issue. I think Passivhaus buildings need as much thought to go into how easy they are to use as goes into the design and construction of the fabric. Although not a problem for us and probably for other early adopters in the UK, it will have an impact on the way Passivhaus is perceived.

Certification airtightness test

Note: since posting this, the completed air test documents show a result of 0.2 air changes per hour.

It's been a while since I've posted during the always-longer-than-the-client-expects period where all the finishing work is completed.

We have started the process to get Certification as a Passivhaus, using the UK's top certifier and general guru on all things building physics related, Warm Low Energy Practice. Yesterday, Paul Jennings ("doorfanman"), our airtightness consultant completed the official airtightness test and we got:

0.19 air changes per hour!

This is a really big improvement on April's test. Partly because I calculated the internal volume more accurately, using Bluebeam, which has a great tool for measuring dimensions, areas etc of PDF plans. Our internal ventilation volume is 442.38m³ and the April test had been based on a rougher calculation of 400m³. Mostly though, the information from the April test helped us to to improve the weak areas.

It will be interesting to see how durable our result is. We believe we have created an airtightness layer which lasts.

I had already put up a DIY shelf in one of the rooms before yesterday's test was conducted, which required drilling a few holes into the plaster than forms the airtightness layer in the external walls of the refurbished part of the house. I put some sealant into the holes before inserting raw-plugs. Obviously, I will be aware of the need not to drill holes in the original external walls without thinking about airtightness. In the new build section, where the airtightness layer is beneath a 50mm service void, I will not have to worry nearly as much about affecting airtightness. For this reason, in any new build, I would always want to design in a service void. I think that, in the real world, it stands a much better chance of remaining intact over the design life of the building.

Next week, our MVHR (heat recovery ventilation unit) will be commissioned. This will involve, amongst other things, calibrating the airflow to each supplied room (and from each extracted room) to:

a) ensure that there is an appropriate air change rate for the use of the room
b) ensure that sufficient heat is delivered to the rooms (the tiny trickle of heat needed in a Passivhaus is delivered via the supplied air in the ventilation system)
c) ensure that the total rate of air supplied equals the total rate of air extracted. This is important because if the two are not in balance, the MVHR wastes electrical energy and because it results in the house being slightly over or under pressure, it will increase the flow of air through the fabric of the building.

0.4 air changes per hour!!

Our airtightness test went really well yesterday. The team achieved a fantastic result of just around 0.4 a.c.h., probably a bit lower, based on an internal ventilation volume of 400m3 - all the more impressive as this is the first build of this type they had worked on, and because more than half of the build is retrofitting the original structure.

We should be able to improve on that figure in the final test needed for Certification, as we were able to identify the relative weak points.

We spent a little time today working out how much extra time we spent into doing tasks that were necessary to achieve it. Our conclusion was that it was not a significant extra task. However, everyone in our team are really committed to paying attention to protecting the airtightness layer. We have not had to have a formal "Airtightness Champion" trying to watch everyone constantly, in case it was damaged.

Watch a clip of the airtightness test on YouTube: http://www.youtube.com/watch?v=nMTLfj4iXec