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Can WUFI Passive help determine if temperatures across rooms will be consistent?

mjezzi | Posted in PassivHaus on

Hi, I’m in zone 5b (Colorado, 7500 ft elevation).

I was wondering if anyone here had experience with WUFI passive and knew if it could tell me that one room will get hotter than another? Or any other technique that would help me figure that out. I want to make sure that the whole house heats evenly from solar gain. I’m planning on reaching passive house standards and have almost eliminated all windows on the east and west sides. Really it’s just a matter of know how much glazing and thermal mass each room needs. Maybe this really isn’t a concern, and if you know that, please let me know.



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  1. brendanalbano | | #1

    I'm pretty sure WUFI Passive isn't really designed to do that. It's a pretty focused program, that is mainly designed to validate if a building meets the PHIUS Passive House standards or not.

    The full version of WUFI, as well as other energy modelling engines like Energy Plus can probably simulate that sort of thing, but are potentially overkill.

    I don't think it will be able to account for thermal mass, and hopefully someone more familiar will correct me if I'm wrong, but the standard Manual J calculation for sizing an HVAC system should be able to give you a sense of the heating and cooling loads of different rooms.

    If you really want to simulate the hour by hour/day by day temperatures generated by your passive solar windows and thermal mass scheme, that's a pretty serious simulation. I believe the Energy Plus energy modelling engine (combined with the Radiance daylighting simulation engine) has the capability to perform that sort of simulation, but I'm not sure that there are any use friendly front-ends to actually set up your inputs and get the outputs you want.

    All that said, I believe the conventional wisdom these days is that super-insulated > mass-and-glass. So you may be just fine making sure you've got a good thermal envelope, keeping your windows modest, and including some shading elements for the summer, without having to do all the fussing involved in a passive solar scheme.

  2. Robert Opaluch | | #2

    You have done heat loss and solar gain calculations. Do them on a room-by-room basis. Also model appliance and electrical "waste" heat; and infiltration, venting & HRV/ERV heat losses in winter, per room. Kitchens can generate a lot of heat. I model hour by hour gains and losses to get an idea of daily peaks and valleys in net heat losses-gains. Not perfect but helps estimate the temps you may experience on sunny winter days with your design. Generally afternoons will reach the peak temp in your south-facing rooms except kitchens, at dinnertime. Dawn will be the minimum temperature without auxiliary heating. Even the first hour of sunlight midwinter in Colorado added 1 degree F in my passive solar home, with less glazing than your window walls.

    4" concrete slab or other substantial thermal mass might keep interior temps in 10 degree range. You can run HRV/ERV on bypass mode to vent excess heat during sunny winter afternoons when interior temps get into high 70'sF whenever you find that uncomfortable. You could let bedrooms go higher to store more heat in thermal mass. I don't know of any precise measure of estimating temperature fluctuation suppression from thermal mass. But I don't think thermal mass will carry you through the night until morning if you aren't willing to tolerate about a 10 degree fluctuation, or more if you use less thermal mass than 4" slab.

  3. mjezzi | | #3

    Hi Brendan

    You’re right, super insulated > glass+mass, but I have views that I want to take advantage of, so I want to figure out how to dial in as much glass as possible. Spending money on more advanced calculations to create a comfortable home with glazing to take in the views will be well worth the effort.

    Hey Robert!

    The biggest difference between my calculations and Wufi passive calculations is that wufi passive can include thermal mass and is probably more accurate in general. By accepting PHIUS standards, we’re accepting the 68-77°F temperature swing.

  4. mjezzi | | #4

    Doing a bit more research, I was able to answer my own question. Yes, you can do room by room energy modeling with WUFI Passive by using "zones".

  5. Jon_R | | #5

    Nothing short of a zoned heating system is going to make a closed off north room the same temperature as a south facing room. An open floor plan will help and even open doors will help some.

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