PH Notes:
Preliminary paper title: “Use of thermal storage in very low energy housing
standards.”
In paper:
- Use detailed energy analysis, LCA, and LCCA (are these latter two the same
thing?) to investigate this?
- Investigate this with regard to the two most prominent (currently) low
energy housing metrics/standards – NZE and Passivhaus.
- Compare three housing types – a cost optimized NZE building, a Passivhaus,
and an IECC 2009 code-compliant house(?)
>> Homes for a Changing Climate:
- Seven ‘principles’ of PH design
o Superinsulate
o Eliminate thermal bridges
o Make it airtight
o Specify energy or heat recovery ventilation
o Specify high performance windows and doors
o Optimize passive-solar and internal heat gains
o Model energy gains and losses using the PHPP
- On how much insulation is required in a PH: “How well insulated? That
depends, of course, on the climate. The achieve the Passive House standard,
Nabih Tahan’s house in Berkeley, CA, required only 6 inches of blown-in
cellulose insulation, while the Skyline Hose, in the far harsher climate of
Duluth, MN, needed 16 inches – almost 3 times as much. Often the first
feature of a Passive House to catch a visitor’s attention is the unusual
thickness of the walls. “ (p. 10)
- On choice of wall assembly: “Even with this insulation requirement, Passive
House designers have a wide range of choices for the materials used to create
superinsulated building envelopes. Wall assemblies can be built using
conventional lumber or masonry construction, double-sutd construction,
structural insulated panels (SIPs), insulated concrete forms (ICFs), truss joist
I-beams (TJIs), steel, or strawbale construction. Similarly, designers can
choose from a number of different types of insulation. These include
cellulose, high-density blown-in fiberglass, polystyrene, spray foam, and –
again – strawbale. Although spray foams have a high R-value and are easy to
apply, many builders prefer not to use them, because they are petroleumbased products, and because the foaming agents can deplete the ozone layer
and contribute to global warming.” … then Vacuum Insulate Panels (VIPs)
are mentioned. (pg. 10)
- On thermal bridges: “When the thermal bridge coefficient, which is an
indicator of the extra heat loss caused by a thermal bridge, is less than .01
W/m-K, the detail or wall assembly is said to be thermal bridge free.” (p. 11)
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On airtightness: “At a standard test pressure of 50 Pa, a Passive House must
allow no more than 0.6 ACH in order to achieve certification. Passive Houses
built from timber, masonry, prefabricated elements, and steel framing
members have all met this standard….Airtightness does not mean that you
can’t open the windows! Passive Houses have fully operable windows, and
most are designed to take full advantage of natural ventilation to help
maintain comfortable temperatures in the spring, fall, and even summer,
depending on the local climate.” (p. 12)
“Well, a Passive House does breathe – exceptionally well. However, rather
than breathing unknown volumes of air through uncontrolled leaks, Passive
Houses breathe controlled volumes of air by mechanical ventilation.” (pg 12)
“In summertime, and in primarily cooling climates, it is very important to
prevent excess solar heat gain, This can be done by shading the windows.
Roof eaves of the proper length can effectively shade south-facing windows
when the sun is higher in summer, and still allow for maximum solar heat
gain in winter, when the sun is lower and the days are colder. Deciduous
trees or vines…” (p. 15)
On the insulation in the Florida PVRES house: “In conventional residential
construction, masonry walls in Florida are insulated with R-3 to R-5 thin
fiberglass batts or XPS, installed on the interior of the wall. Although R-3 to
R-5 may seem quite low for those used to building practices in northern
climates, field monitoring has shown that insulation installed on the interior
of a wall can reduce the need for air-conditioning by only 5% to 10% in
Florida’s climate, if the walls are already a light color. Adding more
insulation to the interior of the wall will further reduce the energy used for
air-conditioning by only 1% or so, because walls in a single-story home with
good overhangs represent only a small part of the cooling load. However,
insulation installed on the exterior of masonry walls can help reduce the
need for air-conditioning during the late afternoon and early evening by
increasing the time that a precooled building can stay comfortable without it.
FSEC chose to pursue this strategy for the PVRES, particularly since
precooling could be accomplished efficiently by running the air-conditioning
in the late morning, when there is usually plenty of sunshine and PV output is
approaching its maximum. By covering the outside of the concrete block
walls of the PVRES with 1.25 inches of isocyanurate insulation, and
increasing the R-value of the wall assembly by R-10, FSEC was able to reduce
the size of the air-conditioning system and shift utility energy use to nonpeak
hours.” (pg 72)
On the Berkeley house: City planning wouldn’t let him make the overhangs
bigger, so: “On the hottest summer days, he opens the windows early in the
morning to cool the house. In the afternoon, when the sun moves to the west
side of the house, he opens up a large umbrella on the deck to shade the
west-facing windows.”
>> Feist paper:
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The envelope insulation helps with comfort – it means that you don’t have to
put radiators in front of the windows because you’re not losing a lot of heat
through the windows.
Space heating demand on same order as solar gains – how do they capture
and store/distribute those solar gains?
o Right now, there’s no passive house provision for thermal mass…but
what if there was? Shouldn’t there be a provision about appropriate
use of thermal storage?
o Can we especially make the case for this using the “summer”
argument – PH not designed for warm climates? If mass especially
needed in warm climates?
o Likewise, in net zero, make the case that thermal storage helps. AND
that it’s cost effective from an LCA/LCCA standpoint.
Mentions that solar protection is essential during the summer and that night
ventilation can be very useful (although ventilation rates too low to provide
actual cooling).
Discusses the ventilation strategy in good detail.
“If building ventilation system is to be used outside of the heating season,
heat recovery is not supposed to be used. Could manually exchange for a
dummy cassette or could bypass heat exchanger.”
Used CFD and test chamber experiments to look at thermal comfort.
>> Hastings paper:
- Discusses cost effectiveness of PH strategies. Lists specific costs for different
strategies.
- Suggestion that regulating temperature in these buildings is different:
“Regulating temperature can only be done by changing fresh air supply,
which changes the balance of the whole system…”
- “Night set-back saves little energy. Because of the high insulation levels, such
houses cool down very slowly…Setting the thermostat drastically back, i.e.,
10 K, during a winter holiday can be problematic upon returning to the
house. The very small heating capacity will result in a very slow heat-up of
the house, of course all the longer if the house is massive.”
- Good discussion of thermal comfort preferences in these houses.
- Good discussion of comfort in summer. Shading critical; critical to keep
house closed up during day, and ventilate at night when cooler. Monitored
example of Vauban apartments.
o BUT: What if it’s a cooling-DOMINATED climate, where heating
doesn’t feature into this much at all? Does it still make sense to shade
and close up the building? Given that the ventilation rate is so
low…probably not. Could mass help?
- Massive hypocaust floor in Rychenbergstrasse apartment
- Summer advantage of mass used in the Vauban apartments
- Also, several of the apartments looked at here had massive wall construction.
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“Mass in such highly insulated buildings is useful for providing better
summer comfort, as was learned from monitoring the Vauban and
Marsbachhohe apartment buildings.”
o Does the mass help preserve cooler temperatures from night vent?
Exactly what is it doing?
>>2004 EDU
- Good detailed info about Klingenberg-Smith house construction details.
- HRV from Germany has sophisticated controls that choose between an earth
tube or an air OA intake.
>> 2007 EDU
- Good detailed description of second PH in Urbana.
- Earth tube from first house is not all that useful.
- Suggestion about net zero issues.
>> 2008 EDU
- Suggestion that if you don’t need a heat-recovery ventilator (like in San
Francisco), you can just build the house with operable windows.
- Does this bring up other control issues?
- Window spec definition is currently based on thermal comfort.
- Suggestion that you should still provide cooling with the heart recovery
ventilator.
>> 2008 Salant
- Danny Parker on the characteristics of a PH in Florida
- Reflective roof, tile floors.
>>2008 Rosenthal
- “Researchers are looking into whether the concept will work in warmer climates –
where a heat exchanger could be used in reverse, to keep cool air in and warm air
out.”
>> 2008 Schiano-Phan
- Suggests that several key PH features (e.g., heat recovery, tight building) are
not needed in the UK climate.
>> Passive-On
- Summer cooling criteria depends on way that cooling is provided (Active vs.
Passive). [pg. 6]
- PH rules in hot climates [pg 5]
- Correction should be made for air velocity provided by nat vent or fans.
- PH design examples
>> ALW: Could work on highly efficient energy and controls systems/strategies for
housing(?)
>> For sensors class: work on something that could be retrofitted into AC units that
can sense comfort conditions better! [[could then do surveys on Cambridge
government workers…]
-- Step 1: Design models
- Start with basecase – what is different about it to make PH? What is
different about it to make NZE?
-- Step 2: Run models…calculate thermal time constant for the houses…explore use
of mass (start with only interior-exposed mass? No “mass” in envelope)