Posts Tagged ‘passivhaus’

Insulating effect of curtains

We’re looking at windows at the moment, and trying to work out what will fit into our budget while giving us the best possible insulation effect (U-Value). The PassivHaus standards state that our windows should have a U value of <= 0.8 W/m2K, so we’re going to try and get as close to that as possible.

It has been suggested that, rather than going for PassivHaus certified triple-glazed units we should go for double glazing and put up some insulated curtains. I’m not sure that would work for every window we have, but it could deliver real cost  savings if it can deliver a decent U-Value.

Not surprisingly, very few people are prepared to put a U-Value on curtains! But I found this great table over at Action 21. It compares the different U-Values for windows alone, and then the total U-Value if using heavy curtains or insulated  shutters.

Window U-value [W/m2K]
Window only
(daytime / nighttime)
with heavy curtains
(nighttime)
with insulated shutters (nighttime)
Single glazed 4.5 3.3-3.6 2.6-3.1
Double glazed, 12mm cavity 2.8 1.9-2.3 1.3-1.7
Double glazed, 16mm cavity, low-E 2.0 1.2-1.6 0.7-1.1
Triple glazed 2.5 1.7-2.1 1.0-1.4
Triple glazed, 2 low-E, Argon filled 1.7 0.8-1.3 0.4-0.8

So it looks like we could get down to 1.2-1.6  with curtains – it’s not 0.8, but it’s pretty close, and according to this table is lower than standard triple glazing.

So this is well worth consideration – but what type of curtains would we need to get those results? Here’s what the Yellow House have to say:

Ecodesign books sometimes talk of “insulating curtains”. These would have to be home-made curtains of insulation sewn between fabric. In order to avoid downdraughts from the window they must fit snugly into a pelmet at the top and a tuckslot at the bottom. In theory an insulating curtain with 60mm mineral wool reduces the u-value of a double glazed window by 75% to 0.6. However they very hard to clean, and there are potential health issues with sharing a living space with mineral wool. A better option might be to convert old duvets into curtains, or make insulation shutters from timber and insulation sheeting. Our feeling is that all these options represent a major intrusion into the living space and are not appropriate for a normal house – though they would be justified in a solar house where there are very large areas of glazing.

Duvets at Sainsbury’s are now incredibly cheap – so maybe that’s what we’ll go for – I’ll chase up prices against triple-glazing.

Resources

Insulation: Understanding R and U values

The more I get into looking at insulating our house, the more I need to learn! At the moment I’m fighting off a swarm of mismatched R, U, and k values. All I want to know is what type of insulation we need to come close to the PassivHaus standards but everything I see is quoting differing units. So what are all those units? and what’s the relationship between them?

What are R,U and k

  • k is the Thermal Conductivity of a material, so for Insulation LOWER is better. Units are W/mK.
  • R is Thermal Resistance of a specific piece of insulation, we want this to be as high as possible. Units are Km²/W. It is calculated as d/k where d is the thickness of the insulation and k is the Thermal Conductivity.
  • U is the Thermal Conductivity of a specific piece of insulation or building element and, as with k, lower is better.  Its units are W/m²K. It is calculated as 1/R or k/d. 

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

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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