Archive for January, 2009

PassivHaus Building with SIPs – Structural Insulated Panels

MySipHouse

MySipHouse

Looks like our dream house may be an as-PassivHaus-as-possible extension of a traditional 3-bed semi. So now I’m looking at how we make that happen. One of the things I’ve come across are Structural Insulated Panels. Essentially these are a thick “sandwich”, with two wooden panels separated by a thick layer of insulating foam. One of their advantages is size – you can get panels up to about 6m long, factory-cut to your dimensions, with all the window and door holes pre-cut. And that means that you can have a very short on-site build time – some SIPs builders claim to be able to have the house built in under a week. It also means you have less joints to compromise your insulation and airtightness.

While they are not all natural – the core is plastic – they do have several real positives:

  • All the  offcuts can be recycled at the factory – no skip required!
  • They use up to 50% less raw timber than a timber-framed house
  • They can result in thinner insulated walls than other methods – 150mm vs 250mm for a cavity wall
  • A typical U Value would be .22 w/m2K – heading for PassivHaus standards

There are lots of considerations when using them though:

  • You need to do all your planning up-front.
  • Use an architect and builder with SIP experience or you’re in for a world of (expensive) pain  caused by last-minute changes.
  • Try to ensure as much of the electrical and plumbing work is done on the internal walls to reduce the impacts on the insulation
  • Ensure that the builders seal all joints correctly with insulating foam (urethane) 
  • You may need to use a vapour barrier to prevent condensation inside panel, which could lead to rot.

They certainly seem to tick a lot of our boxes – they’ll go on the list as a possible option.

Resources

Cheaper Solar Panels (update)

Having posted about predictions that cheaper Solar Panels were on the way in 2009 here we are, less than a month later, and cheaper panels are popping up. OK I’m prepared to admin that this might not be a great economic shift – it might just be that I missed this supplier last time. They are Japanese-made Sharp panels and they are £2.99/Watt. I’ve updated the table of prices below – no other prices have changed, but the 200w Kyocera seems to have dropped off the market. Still a little way to go before we get down to the forecast $2.50/Watt!

EDIT – I’ve also added Navitron to the list – not sure how I missed htem first time. Keen prices at £3.72/Watt.

Supplier Manufacturer Watts £ inc VAT £/Watt
Eco-nomical Sharp 180 538 2.99
Navitron Navitron 110 409 3.72
Wind and Sun BP – 3 Series 160 669.3 4.18
Wind and Sun BP – 3 series 170 727.95 4.28
Marlec BP – 3 Series 125 536 4.29
Marlec BP – 3 Series 135 579 4.29
Wind and Sun BP – 4 Series 175 772.8 4.42
Marlec BP – 3 Series 80 358 4.48
Unlimited Power SunPower 90 471.5 5.24
Unlimited Power Sanyo 215 1331 6.19

How much firewood should you store?

Good Size Log Store

Good Size Log Store

Huge numbers of people are putting in Wood Burning Stoves, Boilers and Ranges at the moment. They’re doing this for a number of reasons: to beat rising gas and electricity prices, to reduce their carbon footprint,  or to improve the resilience of their heating system in the face of peak-oil based supply issues.  The first challenge appears to be actually getting hold of a stove – apparently Dunsley have a 6-month backlog on orders for some of their stoves, And Stovax reported a 50% increas in orders in the last quarter of 2008. Once you have your stove though, how resilient is it likely to be? Unless you have your own woodland you are dependant on a supplier – so will there be enough wood for everyone who is currently putting in a stove or range?

The Guardian recently discussed the problems there are with firewood supply, and there are some of the facts:

  • Current UK consumption is about 1,180,000 tonnes a year.  Only 1m of those are produced in the UK, so we’re currently importing 15% of our firewood needs.
  • However, if you’re not fussy about what you burn, then there are 2.5m tonnes of burnable wood going to landfill every year – so if you see a skip full of random timber or broken pallets take it home and burn it – you’ll be helping the UK become firewood-independant.
  • Demand is increasing at around 25-30% a year, and resulting shortages resulted in price increases of up to 30% at the end of 2008.
  • The increase in demand is particularly resulting in an increasing supply of green, un-seasoned logs that will need to be stored for at least a year before being burnt.
  • There are wide price variations across the UK firewood is most expensive in the North and West, and cheapest in the South East.
  • The Government is working to bring another 2m tonnes of firewood to market by 2020. They say this will be enough to heat 250,000 homes (an average consumption of 8 tonnes/yr/house).

With the current supply chain under significant stress, the easiest way to ensure that your wood-fired stove or boiler continues to provide heat is to make sure that you have stored enough wood yourself. The general guidance is that wood should be stored for a year to reduce its moisture content from the 70-50% it is when felled down to an ideal <25% for burning. If you haven’t been through a full season with your wood-burner yet the general guidance is that an average house will consume 8 tonnes a year – around 12 m³, depending on your level of insulation, how hot you keep the house, whether it’s also heating your hot water etc. So – how much wood have you got stored? Two months supply? Less?

If your wood-burning stove is essential to your heating/cooking/hot water then you need to take wood storage seriously. Build a wood store – a shelter with a roof (clear if possible), open sides, and use pallets for the base and to divide sections to maximise airflow. Preferably split it into at least two sections so that you can have one section “seasoning” (drying) and one section that you are burning. Store the wood end-on to the airflow after chopping it to the right size for your stove. Make the stack as tall, long and thin as possible to maximise airflow.

Do that, and your wood-burning range can provide a really resilient solution to your heating, hot water and cooking needs.

Resources

Bin your Aga – buy a Rayburn

 

An Esse, not an Aga

An Esse, not an Aga

George Monbiot in the Guardian is launching a campaign against the Aga. He reasons that they use a ridiculous amount of oil, and generate an obscene level of CO2. I have to say that I’m with him on this. You won’t find much about Agas on GentleDescent because once I’d done the basic research and found that you couldn’t get a multi-fuel version I realised they weren’t going to meet my post-peak-oil needs. The decision was helped by articles like this one in The Times about people ditching their Agas

 

If you’ve heard about peak oil at all then surely putting in an oil-fired Aga is profoundly stupid. It’s OIL-FIRED. So when oil runs short or is out of your price range then what are you left with?  A great useless lump of cast iron, and no heating or cooking options – not very resilient! If you have to buy an Aga then at least get a Gas or Electric version, but realise that you’re doing it as a lifestyle choice, it is not a resilient long-term option.

So what should you get? I’m still working that out! The couple in the Times article went for a wood-fired Esse with a back boiler.  Ive looked at some really beautiful wood fired stoves, and the Rayburn, paired with a Solar Thermal system, but I’ve yet to come to a conclusion.

But what should you do if you do have an oil-fired Aga already? Apparently their re-sale valus is terrible, so I guess if you were feeling optimistic you could convert it to Gas, which may last a little longer, and be a little more environmentally friendly. Twyford do official Aga Gas Conversions. Otherwise? Send it for recycling. And buy a Rayburn (probably).

Peak-Oil Kitchen Gadgets – Slow Cooker

thermax_slow_cooker

An interesting one this – a slow cooker based on a thermos. Basically you heat up the pot of food and then pop it into the insulated flask. It’ll keep cooking for eight hours. Think of the energy you save – it only needs to be on the stove for about 20 minutes to cook a whole dinner.

thermos-shuttle-chefHere’s what one actually looks like – the 4.5 litre “Thermos Shuttle Chef” – and you can get them from Amazon for under £80.

A Passivhaus (Passive House) renovation?

passivhaus_thermogram_gedaemmt_ungedaemmt

The picture on the left is a thermograph – showing the difference in lost heat between a conventional house (on the left) and a house built to PassivHaus standards (on the right). Which house would you rather be living in when Russia cuts gas supplies

The PassivHaus standard, as interpreted for the UK by the AECB, should result in an 80% reduction in a house’s energy consumption. PassivHaus design concentrates on three areas: improving the air-tightness of the house, reducing heat bridges, and, to a lesser extent, considering heat gain from the sun.

In essence, a typical passivhaus is air-tight & super-insulated, with mechanical ventilation with heat recovery (referred to as MVHR) to solve the issue of internal air quality. I had always believed that a PassivHaus needed no extra heating, but apparently that’s not entirely true. While they’ll generally have no radiators or underfloor heating, they often do have a small heating element within the ventilation system. In general they require about 30cm of insulation, and windows that are triple glazed.

Here are some of the key points of interest to me from the AECB version of the standard:

  • Use daylight to displace use of electric light
  • Solar hot water system required to deliver at least 50% of hot water
  • Walls, Floors, and Roof to all have U values of <= 0.15W/m2K
  • Doors (uninstalled) should have a U value of <= 0.6 W/m2K
  • Windows (uninstalled) should have a U value of <= 0.8 W/m2K, with a solar energy transmittance (inc frames) of >= 35% and a visible light transmittance (inc frames) >= 50%
  • Rooflights (uninstalled) should have a U value of <= 1.0 W/m2K
  • All habitable areas to have a glazing area (excl frames) >= 14% floor area
  • Typically space is heated with hot water coils within the MVHR ducts
  • MVHR should recover at least 75% of heat, with a fan using <=1.44W per l/s
  • Any non-solar water heating to be Gas Condensing boiler or CHP – wood fired stoves are not permitted (this conflicts with my peak-oil resilience planning)
  • Insulation on water tanks to be at least 100mm PU foam, all pipes and valves to be insulated with at least 40mm mineral fibre, and all cold pipes to have a vapour barrier
  • Lighting to be >= 50lm/W
  • Use the most efficient appliances – A/A+ minimum. TV to be LCD.
  • Use a heavy-duty membrane to air-proof the house.

In conclusion, this is a great list of targets which I may I don’t think I’d go for PassivHaus certification, even though I like the overall aims – my Peak-Oil resilience planning needs things that are proscribed by the standard – like a wood-fired stove!

 PassivHaus Resources

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