We've got a 5 storey wood frame building pursuing LEED Silver. Our current dilemma is we have large and long units. Approximately 80% of the suite can be natuarlly ventilated to ASHRAE 62.1-2004. Our problem is the 25' rule within the same space, which in our cases are dens and kitchens. The dens have no door and have a permanent opening as required by ashrae but the farthest wall is not within 25'. I'm sure some people have run into this problem, I see some people have put transfer fans in their units, how exactly was this designed?
Currently our design incorporates a geothermal water to air heat pump c/w with a 4" round outside air duct ducted to the return air duct of the heat pump. We also have a continuously running HRV exhausting from each suite and supplying fresh air to the corridiors. I realize this is a hard thing to input on the energy models (so i've been told) and we may incur an energy penalty for reheating outside air for each unit, the project energy modeler is in the midst of modeling this to ensure we still get our requried energy points.
Has anyone been successful with the proposed system above or have an example of something that has been successful?
Thanks,
Alex
Alex Wong
20 thumbs up
May 10, 2010 - 5:27 pm
Sorry i forgot to add that the HRV will only supply approx 70% of the required O/A. The rest of the portion is by fresh air duct to the heat pump and/or openable windows. Is this too complicated? Can we pass with just openable windows and make-up from the corridor?
Roger Chang
Principal, Energy and Engineering LeaderDLR Group | Westlake Reed Leskosky
LEEDuser Expert
398 thumbs up
May 12, 2010 - 4:36 pm
Alex, I have some experience using transfer air to meet 62.1 requirements. You have to look carefully at the classification of air (1, 2, 3, 4). 62.1 allows you to transfer air, as long as classification of air stays the same or goes from lower to higher (cleaner to dirtier). You may be able to use the OA from the HRV to ventilate the 20% that is not covered by natural ventilation.
Alex Wong
20 thumbs up
May 14, 2010 - 4:52 pm
Thanks for your reply Roger,
I think the confusion we are having is there is no prescriptive method to prove you are meeting ASHRAE 62 by means of partial ventilation and natural ventilation. It seems on the diagram at the top of the page if you have a mixed system you must meet 100% of the mechanical ventilation (VRP). But even if you have 95% of the openable window area required by section 5, we are still required to meet the rates required by the ventilation rate procedure. Does this seem a bit over kill?