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DEAP and HRV systems

  • 19-05-2009 02:19PM
    #1
    sydthebeat
    Subscribers Posts: 42,642 ✭✭✭✭


    Why is the DEAP methodology so hard on Mechanical Heat recovery Systems?

    Frequent users of DEAP may find that changing from a natural vented system to a MHRV system sometimes adds on energy usage and equates to a worse rating, this can be frustrating when the advantages of MHRV is well known....

    well, ive found certain factors need to be inputed to show a real advantage for MHRV:

    1. DO NOT USE THE DEFAULT FIGURES
    The are terribly short of 'real' SAP appendix Q figures. The figure of 2.0 w/l/s is woefully out of touch. Find actualy SAP figures and input them. I find the default figures can severly hinder the resultant performance and your ability to argue for a HRV system to be installed.

    2. ASSUME A 'DECENT' AIR TIGHTNESS RESULT.
    This will commonly mean the implementation of some kind of air tightness scheme. Include for this in your specification. Timber frames will need a comprehensive air tightnes scheme, whereas block build can use teh plastered blockwork as a continuity layer, so its just timberwork that needs to be membraned. The difference between a Q50 of 7 and 5 can be as much as 5 kw/hr/m2. Always aim for at least a 7.

    3.Use either dampers on flues, or room sealed stoves
    Chimneys without dampers are assumed to loose twice the heat as flues with dampers.

    4. Intermittant fans by HRV system
    Design as much intermittant fans into the HRV system a will be allowed by the system. These then are not required to be separately inputted as intermittant fans. This is something that the HRV system does anyway, just remember not to add them separately. Sometimes, that generally only leaves 1 intermittant fan, that being from the oven hood.

    5. Design a draught lobby where possible
    At these energy levels, a draugh lobby can make a significant saving (approx 3 kw/hr/m2). In my opinion these should always be included. Air infiltration due to openings is almost halved because of this.



    Including all these on a 2008 reg house can mean the difference of approx 11 - 13 kwhr/m2/year saving on your energy rating, depending on the form of your dwelling (single storey dwellings tend to do worse).
    As many 2008 reg dwellings will be in the range of B1-B2, this can mean the difference in an improved rating catagory almost on its own.


Comments

  • #2
    sinnerboy
    Closed Accounts Posts: 5,433 ✭✭✭sinnerboy


    Great post . Thanks Syd .


  • #3
    Chimpster
    Closed Accounts Posts: 146 ✭✭Chimpster


    sinnerboy wrote: »
    Great post . Thanks Syd .

    Good post Syd.

    If your going with HRV try its foolish not to try and get it below the 2 m3/hr/m2.

    Provisional testing is the key.

    A common problem is that alot of people are going with standard 4 inch cavitys and using dry ling insulation to get a decent U value. Whilst we always recommend a scratch coat on the inner side of the external walls only a minority of clients actually do it due to cost so the provisional test results are usually quite poor.... and guess what so are the final results.


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