Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)


Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!

powered by Surfing Waves

Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.

    • CommentAuthorLeo
    • CommentTimeMay 18th 2007
    I'm in the process of measuring my house to do heat loss calculations throughout. I haven't done this before and a couple of things have struck me:

    All the sources I've seen on this give air change figures that appear to be taken 'as standard' from I don't know where. This may be fine dealing with new build where there is design intention for specific rooms to have specific ventillation rates, but is there some way I can make a more informed estimate for the rooms in my 1880s house?

    Further to this, a number of rooms on the ground floor have been knocked through at some point. This includes open plan access into a glass-roofed kitchen extension, that I'm guessing wouldn't pass regs today. Airflow is therefore hugely important in working out where all the heat is going. Rather than treat this interconnected area all as one room (which it isn't) It seems sensible to treat the regions as separate rooms. This would also allow me to model what happens if I re-partition them in various ways, as well as telling me if the existing rads are sized correctly for the current layout. But how do I work out air changes based on the size of the openings between them?
    Hi Leo, Can I ask what software you plan to use for this? In my experience only dynamic simulation software allows you to estimate ventilation heat losses with accuracy [and even then its still only a model!]
    to do any serious calculations you need to get a copy of SAP 2005, free from DEFRA on 0845 120 7799 or (www.bre.uk/sap2005).
    Air changes are quoted at Appendix P (assessmant of internal temperature in summer). For houses the figures quoted for 2 storey houses with cross-ventilation possible / not possible are: trickle vents only 0.2/0.1, windows open 50mm 1/0.6, windows open fully 8/5 air changes per hour.
    • CommentAuthortony
    • CommentTimeMay 19th 2007
    The problem with this notion is that at current building regs allowable air infiltration rates ( air tightness if it can even be called that) we are talking about all the small gaps and cracks etc adding up to almost the same as having a window open all the time and in some cases a door!

    Do you think SAP can be anywhere near accurate for calculating losses due to air infiltration?
    • CommentAuthortony
    • CommentTimeMay 20th 2007
    No -- well may be it might be close if there was no wind and it was not cold outside.
    • CommentAuthorLeo
    • CommentTimeMay 21st 2007 edited

    I wasn't planning to use any particular software. I was hoping to get away with doing it on a spreadsheet, looking up u-values from various sources. I'll have a look at SAP and see if that helps. I've looked at a couple of flash-based freebies like the one on www.heatweb.com, but they don't seem to do anything a spreadsheet won't and are less flexible. Any more info on free software or air movements gratefully accepted.
    • CommentAuthorLeo
    • CommentTimeMay 28th 2007
    I've looked at SAP 2005 now. It seems helpful in working out overall losses for the building (using the reduced dataset), but doesn't help me with my internal distribution much. Perhaps I'll try 2 separate calculations - one including the glass extension and one pretending it doesn't exist.
    • CommentAuthorken davis
    • CommentTimeMay 28th 2007
    i can not understand why you might want to do this because in a house of that age you will not be able to meaningfully estimate what you infiltration losses (through the fabric and its gaps) are unless you have constructed a complete plastic bag around the house and had a pressure test done. what are trying to show?
    Sorry Mike George for not replying eartlier , but have been away. (Greek island wher newbuild seems to be poured in- situ reinforced concrete with cavity walls but no insulation)
    Yes, I think SAP gives a reasonable average for air changes, but without a pressure test obviously we are only estimating re structural leakage. As you suggest there will be additional air filtration due to general leakage and this will vary from building to building. The "standard" leakage for air pressure test is 10 air changes per hour at a pressure of 50 Pascals; this is for new construction so older houses may well be double this at least. The ach figure under pressure is divided by 20 to give a realistic normal loss, so 20ach would be entered as 1ach in any calcs. In addition open chimneys, catflaps etc should also be included to get as accurate as possible figure.
    • CommentAuthorLeo
    • CommentTimeMay 31st 2007

    The current central heating is a) burning tenners like you wouldn't believe and b) leaving parts of the house too damn cold. I'm trying to work out what's wrong; whether the radiator and boiler sizing is competely up the spout or just needs tweaking (intend to replace boiler in next couple of years anyhow as it was only 65% efficient new in '96) and whether the glass-roofed kitchen extension is a complete liability or can be heated adequately at a reasonable cost. That's all. My interest in air changes relates to air movements between 3 interlinked 'open plan' rooms, one of which is this glass extension that drops to 15 degrees when the others are at about 20. I want to work out if I'm better off increasing the heater size in this extension or giving it up as living space, calling it a conservatory, shifting the kitchen into the main house and putting a door in.
    • CommentAuthorken davis
    • CommentTimeMay 31st 2007
    air movement and infiltration will at best be a very approx. estimate in these circumstances. the glassed roof kitchen is a complete liability, why not put a proper (and much better insulated) roof on it? (perhaps with a double glazed rooflight in the darkest corner) , improve overall insulation and draught proofing first (after the glass roof!) then put TRVs on the rads you already have which should even out heat output to demand in each space. can you, have you, insulated and sealed the floors ....what type are they?
    • CommentAuthorLeo
    • CommentTimeMay 31st 2007
    The kitchen extension floor is solid concrete (unfinished, just sealed). It's quite low, perhaps the previous owners intended putting UFH in. Looks about 5" lower than you might expect relative to doors/ windows. Not sure. We are toying with either UFH, or just insulating and adding a suspended floor on top. Another option is to remove this extension completely sometime down the line and put up a new one positioned to act as a passive solar collector. (The current one is in shade most of the winter and in full sun midday in summer).

    In any case I need some way to 'make do' for the time being (perhaps 2-5 years). Hence the calculations.

    Other floors are suspended wooden floors which we are going to seal. Probably with Gapseal v-strip. I'm just about to try it out in a bedroom. Ground floor void is about 3 ft deep. Have considered blowing in loose insulation but don't know whether damp may be a problem. I'm not willing to pull up all the boards to lay batts between the joists.

    Windows are old and draughty but I intend to use a combination of brush strip which I'm hoping to fit this summer (and I rescued all the original sashes from a house down the street when they fitted UPVC so some of them may be in better condition - a lot of ripping out going on round here, I've just salvaged some moulded skirtings too. Not to mention the fireplaces.) and possibly secondary glazing - I'm hoping to get some quotes in the next few weeks.

    Any further ideas welcome.
    • CommentAuthorken davis
    • CommentTimeMay 31st 2007
    phone me if you wish: 01424 752311
Add your comments

    Username Password
  • Format comments as
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   

© Green Building Press