Case not matching actual site data

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woodenrings
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Joined: Thu Nov 26, 2020 10:11 am -1100

Case not matching actual site data

Post by woodenrings » Wed Dec 23, 2020 3:54 pm -1100

I have energy use and first hand accounts of temperatures from an owner of a classic 1980's double envelope home I am attempting to model in WUFI Passive.
The assemblies are typical of the 80's with the north / south walls being 2x4 + bat fiberglass insulation and a 1ft minimal air gap, up to 9ft in one section on the south wall.
The east / west walls are 2x6, bat insulated. Ceiling is an odd combination of truss, bat insulation, air gap, then more bat insulation, then open space.
Basement throughout with 30ft 8" air tube in basement only opened during hotter times of year.

I have tried to model the home several different ways so far with a goal of ~20 kBtu / sqft yr as teased out of electric bills the individual provided.
The following are all Summer models with shading from trees included, the energy demand is close enough to warrant the quick comparison before moving forward.
  1. Two simulated zones (thermal buffer zone and interior living space) including the basement (256 kBtu / sqft yr)
  2. Same as case 1 excluding the basement. (165 kBtu / sqft yr)
  3. Copies Case 2, Zone with the thermal buffer zone (TBZ) set to attached unheated space. Zone 1 internal living space assemblies all have inner wall + air gap + exterior wall. (80 kBtu / sqft yr)
  4. Copies Case 3, sets TBZ to unheated cellar (77 kBtu / sqft yr)
  5. Copies case 4, sets TBZ to wintergarden with .1 heat transfer [for extremes to see what happens] (64 kBtu / sqft yr)
If anyone has any suggestions as to what else I can try in WUFI to get the model closer to reality it would be appreciated. I realize it is a tough ask since modeling air flow is hard enough as it is and the assemblies with air gaps, while the "best" solution right now, are not ideal since they are assumed to be static and not vented or earth temperature moderated.

woodenrings
WUFI User
WUFI User
Posts: 9
Joined: Thu Nov 26, 2020 10:11 am -1100

Re: Case not matching actual site data

Post by woodenrings » Thu Dec 24, 2020 5:43 pm -1100

Added a couple more cases for extremes ... don't laugh ;)

6. Same as Case 3, replaces all Air gaps with 1:1 thickness polyisocyanurate board ... result, (73kBtu/sqft yr)
7. Same as Case 3, replaces all assemblies with R60 foam board ... result, (72 kBtu / sqft yr)
8. Same as Case 7 but changed the actual blower door test of 1.25 to the recommended max of 0.05 ... result (36 kBtu / sqft yr)

This was just an exercise in absurdities vs reality and still not being able to get to reality even going with what I thought were extremes.

Still seeking suggestions.

woodenrings
WUFI User
WUFI User
Posts: 9
Joined: Thu Nov 26, 2020 10:11 am -1100

Re: Case not matching actual site data

Post by woodenrings » Mon Dec 28, 2020 1:30 pm -1100

9. Same as case 7 but R60's turned up to R96 and the Climate data moderated to represent temperatures expected in the thermal buffer zone ( ~31 kBtu / sqft yr ... blower door set to 0.05 as well ... heating load projected at ~6k which is off by about 1k from reality)

10. Two zones, TBZ not simulated but attached (no heat transfer mod), all assemblies in Zone 1 match reality, Mod climate data to represent temps expected in TBZ, mod airtightness to 0.05 (~42 kBtu / sqft yr ... heating load showing 10.5k

Getting closer to results but further from realty (in case 9)

Max energy usage on site is 9980 during heating months and 5700 during cooling months. This accounts for water heating, aux fans, kitchen / bath fans, several computers, entertainment, and a dehumidifier nearly running full time as a "base load" ...

WUFI still not reflecting reality here :/

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