LCAb Research Outline
Amanda Webb
4 April 2011
Preliminary Title:
Use of thermal mass [storage?] in [achieving?] very low energy housing standards
[metrics?]
>> Could focus more on thermal comfort? Focus more on comfort and mass?
Comfort in PH vs. comfort in net zero vs. comfort in basecase?
Primary Question(s):
- What is the role of thermal mass in helping to achieve very low energy use
targets for single family housing?
o Does thermal mass make a difference in a PH?
 Note that PH standards do not currently require added mass –
if our findings indicate considerable benefit, perhaps they
should?
 Problem with this: Use of mass is a strategy, not a
performance metric, like the rest of the PH
requirements.
 Right now the PH standard doesn’t vary from climate to
climate, but maybe it should?
o Can mass help shape optimization curve (i.e., shift Pt. 3) in NZE home?
Key Background Points:
- Mass has been used in many built PHs to date (indicated in books and
papers)
- Suggestions in papers about adapting for hot climates:
o Belief that high insulation value also helps with heating season
o Heat recovery not needed in heating season (exchange wheel for
dummy cassette)
o Shading is essential
o Can have active cooling, but not necessary if in appropriate climate
o Passive-on sets limits for active cooling, too! (same limit as heating)
 Check out Passive-On documents for this specific data
o Could deliver cooling through ventilation system, or could just open
windows if climate appropriate
- Suggestion that regulating temperature in PH is different, because it can only
be done through the fresh air supply…
- Danny Parker suggestion in one of the articles that adapting PH to Florida
would not be very hard. Use reflective roof/coatings, pay attention to
dehum.
- Note that for costs, While BEOpt stops at a certain point, PH is based on
“tunneling through the cost barrier” – get operational efficiency so low that
you push beyond the point of diminishing returns.
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Suggestion in Newell article that “massive” constuction really has to do with
the time constant of the house – not just adding concrete.
Methodology:
- Make quick reference spreadsheet of PHs built to date:
o In the US
o Utilizing mass
 Reference Passive-On Part 1 designs – how many of these use
mass?
- Double check mass options and modeling methods in PHPP and BEOpt/E+
(are they same? Dfferent?)
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Comparison Tools: energy modeling, LCA, and cost (LCCA)
o Cost already accounted for in BEOpt, so makes sense to continue to
utilize this metric
o Note that some papers have pointed out that it doesn’t make sense to
look at LCA, because operational energy use dominates over lifetime
of a building – but how true is this for PH, or for NZE?
Compare three housing types – compare with and without mass (floor):
o An IECC 2009 code-compliant basecase
o A cost-optimized NZE house
o A Passivhaus
Compare in three climates (based on how US climate differs from midContinental Europe):
o Chicago (colder)
o Phoenix (hotter)
o Miami (more humid)
o Need to include Germany climate for comparison??
Compare interior mass only (i.e., mass not in envelope)
o Could look at mass in envelope later (i.e., after first set of results), but
it has been shown in a couple of studies (including ours) to not matter
than much. – Note that there are no true “mass wall” PHs; all results
show that even where ICF is used, there’s so much insulated
compared to the structural concrete…it would be pointless to look at
the effects of mass or no mass in this type of envelope.
o Also, Laverge paper found no difference in mass wall PH; Zheng
netzero paper found that the mass was actually working against the
house; the PH book talks about the Florida house as having insulation
on the exterior – based on previous monitored experiences.
o Look at adding mass in the floor only?
Need to look at two different cooling methods
o Active cooling (Fanger model)
o Passive cooling (Adaptive model)
“Timeline”:
- Finish research (PH precedents; Mass calc methods)
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Design/Build models
o Basecase – already exists
o NZE – Run BEOpt to get parameters; adjust E+ basecase IDF
o PH – Use PHPP on basecase model to adjust parameters.
 If I input PHPP parameters into E+, is it possible that I’ll get
slighly different results?
 Use ventilation strategies as described in Feist 2005 paper.
Perform LCA/LCCA
Barriers:
- Design for PH: there will be a lot of “design” for the PH house, as PH is not
proscriptive standard.
o How to pick wall system (lots of different kinds have been used)
o Solar protection/shading is essential (how should we design this?
Optimal cutoff?)
 Larger picture of this: Ensuring that the design meets the PH
summer criteria
o Use nat vent or deliver cooling thorugh vent system?
 Summer cooling depends on
o Will need to make the case for why we made these decisions in the
paper.
o Would it be better to base model off an existing, built PH design?
- How to backwards account for thermal bridging?
o E+/BEOpt will not account for thermal bridging, but PHPP will. Do I
need to back-calculate the thermal bridging effects of the other two
designs? Should I use PHPP to test all of the designs?
- How to adjust PH for warm climates:
o COULD just use nat vent. Could also use ventilation system. Which of
these to do?
o Likewise, humidity will be key issue for Miami. How to do
dehumidification in more efficient way? Dessicant wheel?
o Currently, have only come across IDEAS for how to adjust PH in warm
climates. Haven’t come across rules or examples