Case Study Montague

8/3/2019 Case Study Montague

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M O N T A G U E

U R B A N

H O

M E S T E A D . .

ZERO ENERGY HOUSE : CASE STU

MUGDHA S. MOKASH



M O N T A G U E

U R B A N

H O

M E S T E A D . .

LOCATION AND SITE DESCRIPTION

:

HIGHLIGHTS : Walls : Double stud wall

with dense pack blowncellulose.

Ceiling : R-100 blown inloose f ill cellulose insulation

Foundation : R-30 extr uded

polyethylene insulation.

Windows : Maximum southfacing windows with highSHGC

Heatingand Cooling :

Passive ± super insulation,air

tightness,ther malmass,glazing

Active ±mini-split air sourceheat pump,hot air solar

panel Ventilation : HRV with 155

ECM

The Montague Ur ban Homestead is located in the small town of Turners Falls,Massachusetts.

The house is built on a 14,000sq.ft lot which used to be a backyar d, instead of locating it in a p r istine area. The house is a n ew constr uction, squeezed inbetween two existing homes. It is located off a major bus line, and has all the basicamenities available within 3 miles region. These ser vices include a gr ocery store,har dware store, dr ug store, bakery, library, post off ice, banks, parks, etc. Thelocation, thus, helps to reduce the dependence on car indirectly helping to reducethe car bon emissions.

HOUSE DESCRIPTION :

MASSACHUSETTS ±

Average Winter temperature ± 16o F

Average Summer temperature ± 80o F

Annual Heating Degree Days :

6979 (Base temperature ± 65o F)

Annual Cooling Degree Days :

333 (Base temperature ± 65o F)

The house is a single storey, single familydetached dwelling having 3 bedr ooms and

one bath.

The number of occupants are 2, DougStephens and Tina Clarke who are also thedesigners f or the house.The house has a total area of 1152 sq.ft(107.06 sq.m) which is conditioned

alongwith a mudr oom of 96 sq.ft which isinsulated but unheated.The house is oreinted facing south along the

east-west axis. The entry is facing the south.

Majority of the windows are put on the south

façade in order to harvest maximum southern

sun.



Double stud walls, with insulation in between, areusually used f or constr uction in cold climates.

The wall consists of a 12´ cavity with an exter ior 2X 4 str uctural stud wall at 16´ o.c and an inter ior 2 X4 non-str uctural stud wall at 24´ o.c. The cavity inbetween the two stud layers is f illed with densepack blown cellulose insulation by Celluspray(R=45).½´ CDX Plywood sheathing on the exter ior iscovered using Typar house wrap. The purpose of the house wrap is to act as a secondary water

barr ier after the cladding. Typar house wrap thusprevents water fr om seeping into the house. Also ithas an optimal per m rating of 11.7 This ensures theevaporation of any moisture that maybe trapped

within the wall cavity, thus allowing the str ucture tobreathe.Although the house wrap does notcontr ibute in any way to the R-value of wallassembly, the typar house wrap has an exceptionaltear strength, ensur ing a super ior a ir holdout. All theTypar seams are taped while the CDX seams arecaulked.

FSC Cedar shingles dipped in f iltered, boiled

linseed oil are used f or exter ior cladding. Theinter ior surface is f inished using ½´ Gypsum boar d.

B U I L D I N G

E N V E L O P E .

. . .

WALL ASSEMBLY :

THERMAL BOUNDARY :

The climate of Massachusetts

being cold, the ther malboundary is kept as compactas possible. This reduces thevolume required to be heated.

The attic is not accounted f or as a habitable space and

hence is not included withinthe ther mal boundary of the

house. Also, the attic isaccessible fr om the gable end

of the r oof and not thr oughthe ceiling. The ther malboundary, thus, ends at theceiling.A mudr oom located onthe northern side is insulated

but not conditioned or heated.

In case of a double stud wall, the gap between the exter ior framing and inter ior framing acts as the ther mal break, and affects the R-value of the whole wall.However, with impr ovisation f or the r im joist details, more insulation, better airtightness and better insulation f or the f oundation assembly, the R-value can beimpr oved signif icantly.

Materials R value

Outside air film 0.17

FSC Cedar Shingles 0.97

½ inch CDX Sheathing 0.63

Dense pack Blown Cellulose 42

2 x 4 Wood studs for framing 4.38

½ inch Gypsum board 0.45

Inside air film 0.68

R-value for insulation 44.9

Consider 80% insulation 35.92

R-value for framing 7.28

Consider 20% framing 1.456

Total R-value 37.376



The r oof is a standing seam metal r oof with the r oof frame being a conventional pre-manufactured

tr uss. The attic h a s a 30´ of blown loose-f illcellulose insulation above the ceiling. The tr uss hasan extra 18´ r ise at the eaves in or der toaccommodate f or the thick insulation.The standing seam metal r oof also hasconventional soff it vents and a continuous r idgevent. The purpose of these vents is to intake freshair thr ough the eaves in the attic and let it outthr ough the r idge vent. This helps to set up a

continuous air flow in the attic, thus ventilating it. All the ceiling penetrations are sealed fr om aboveusing spray-on-two-part polyurethane f oam.

B U I L D I N G

E N V E L O P E .

. . .

CEILING ASSEMBLY :

PROTECTION AGAINST

TERMITES:

A 14́ wide copper ter miteflashing is glued on top of thef oundation wall, thus,preventing any contactbetween the concrete and

wooden assembly.

The house has a conventional 12´ X 24´concrete f ooting keyed to an 8´ concretef oundation wall or deep fr ost walls which are 4¶

deep. This is the basic f oundation assemblysupporting the 4´ thick slab on grade. A 6´extr uded polyethylene insulation r uns beneaththe slab on grade.

Materials R value

Outside air film 0.17

Polyurethane (foamed in

place) 6.25Blown loose fill cellulose 100

2 X 6 Joist 6.88

1/2 inch Gypsum board 0.45

Inside air film 0.68

R-value for insulation 107.55

Consider 85% insulat ion 91.4175

R-value for framing 14.43

Consider 15% framing 2.1645

Total R-value 93.582

FOUNDATION ASSEMBLY :Materials R value

6" extruded polyethylene 30

4" thick concrete slab 0.32

Total R-value 30.32

2´ thick polyethylene insulation r uns down along the per imeter of the f oundationwall to the top of the f ooting. The concrete slab with the insulation rests on a 12¶¶thick compacted gravel base.

This, thus, ensures an envelope having a continuous insulation blanket with veryfew ther mal breaks.



The ratio of window glazing to floor is 13%. Maximum windows are or iented on thesouthern façade to maximize the solar gain and reduce the heating load. The

windows on the other facades are minimal and positioned f or emergency exit or f or cr oss ventilation.All the windows are tr iple glazed windows.

B U I L D I N G

E N V E L O P E .

. . .

WINDOWS :

ADV ANTAGES OF

CONSTRUCTION ASSEMBLIES :

The type of assemblieschosen f or the constr uctionare extremely apt f or theclimate f or which the house isbuilt. The super insulation of the assemblies helps toreduce the heating loads onthe mechanical systems. Thedense pack cellulose used inwall assemblies and blownloose-f ill cellulose ser ve asexcellent air barr iers. Theextra insulation beneath theslab on grade prevents theloss of heat thr ough the slab

to the gr ound.

The windows on the southern façade are pr ovided with inter ior per manentshutters made of 1 inch thick f oil faced poly-isocyanurate sheets, covered with 18´plywood. These shutters increase the R-value of the window fr om R-4.8 to R-12.

ORIENTATION SHGC U- FACTOR

SOUTH FAÇADE Glass 0.68 0.21

Whole Window 0.44 0.23

NORTH / EAST / WEST FAÇADEGlass 0.37 0.12

Whole Window 0.25 0.17

Comprehensive Passive

Design :

South ± facing windows



V E N T I L A T I

O N

A N D

L I G

H T I N G . . .

PASSIVE VENTILATION :

HEAT RECOVERY

VENTILATOR :

Motor ± 155 ECM

Dual Speed ± 66 cf m / 155

cf m79% Effective

ACH ± 0.4

Power : 34 W at low speed95 W at high speed

LIGHTING :

50% Light f ixture ± pin-based

fluor oscent which meetenergy star and Calif orniaTitle24 Standar d.

Remaining 50% - compact

Ventilation thr ough the house is also aided by the use of a 79% effective HRV i.e

a heat recovery ventilator . The HRV is suspended fr om the ceiling over thewasher in the utility area and it draws exhaust air fr om the bathr oom vents. It thensupplies fresh air to all the three bedr ooms and the living r oom thr ough 6´ wideducts. These ducts are positioned within the conditioned zone. The HRV operatesusing a high eff iciency 155 ECM (electr onically commutated motor) with dualspeed of 66 cf m and 155 cf m fan, pr oviding 0.4 ACH drawing power of 34W atlow speed and 95W at high speed.

The 155 ECM motor used in HRV has the capacity to heat the incoming fresh air by the outgoing stale air to atleast 50o F, when the outside temperature is below

zer o.

Maximum glazing isor iented over thesouthern façade tomaximize solar har vesting. However, theminimum windows on thenorthern, eastern and

western façade,eff iciently facilitatenatural cr oss ventilation.

The inter ior windowframes are bevelled onthe inside which allowsthe captured sunlight tospread at a wider angleand impr oves lightdistr ibution within thehouse.

ACTIVE VENTILATION (HRV) :



H E A T I N G A

N D

C O O L I N G . . .

PASSIVE HEATING AND COOLING :

MINI-SPLIT AIR SOURCE

HEAT PUMP :

Pr ovides flexibility f or heatingdifferent zones thr ough asingle outdoor compressor .

The absence of ducting helpsto overcome the heat lossesthr ough ducts which usuallyaccount f or 30% of the energy

consumption within aconditioned space.

The mechanism operates onelectr icity which is used f or compressing and expandingthe refr igerant in the conduit.

The Montague Ur ban Homestead is an all-electr ic house. Thus, the main sourceof energy used f or space heating is electr icity.

Mini-split air source heat pumps are used within the house f or space heating.These consist of an outdoor compressor and an indoor air handling unit. Theadvantage of these pumps is that ar ound f our air handling units can be attached

to a single outdoor unit. These heat pumps are ductless. The outdoor unit isconnected to the indoor AHU by conduits which carry within it the refr igeranttubing, power cables and suction tubing.

The mini-split air source heat pump can also be r un as a summer air -conditioner and as a de-humidif ier .

The super insulated envelope, air sealing on all sides, ther mal mass of thebuilding constr uction assemblies alongwith the south-facing glazing facilitate

passive heating to a great extent within the house. This, thus, reduces the bur denon mechanical equipments.

Maximum glazing area is positioned over the southern façade f or har vestingmaximum solar energy. All ar ound the house the r oof has an overhang of ar ound2¶ except f or the northern façade where the r oof overhang is just a few inches.

Overhangs over the souther façade pr ovide f ull solar gain dur ing the winter seasons. These allow reasonable solar gain dur ing the shoulder seasons and

pr ovide about 90% shading dur ing the summer season, when the southern solar intensity is more or higher than essential. Trellis style awnings are also added

dur ing the summer . The presence of deciduous trees on the east and westpr ovide shading dur ing the summer months.

Dark black coloured concrete slab within the r ooms helps to absor b the heat of the sun dur ing winter and holds the coolness dur ing summer .ACTIVE HEATING AND COOLING :

Mini-split air source heat pumps -



H E A T I N G A

N D

C O O L I N G . . .

HOT AIR SOLAR PANELS :

Pr ovides 19,000 Btu (5.56

Kw) on a sunny day.The house has suff icientther mal mass to absor b thiswithout overheating.

DOMESTIC HOT W ATER :

Two 4¶ X 8¶ flat platecollectors80 gallon storage tank3kW electr ic heating element

The house has a 2-panel solar hot water system. It uses 4¶ X 8¶ flat platecollectors which are connected to a 80 gallon hot water storage tank.The tank is also pr ovided with a 3kW electr ic heating element.

Hot Air Solar Panels are also used as an alternative active mode of heating thehouse, thus, reducing the reliance on f ossil f uels f or meeting the heatingdemands.

The Hot Air Solar Panel consists of a flat plate glass mounted against a blackcollector plate. The sun shines over the glass war ming the collector plate behind.

The heat fr om the collector is then transferred to the air blown in fr om thebackside. The duct carrying this heated air is connected to a fan motor which inturn is connected to a ther mostat within the r oom. When the air inside the ductgets heated to a temperature higher than the indoor temperature and the

ther mostat detects the need of heating within the r oom, the fan motor activates,dr iving the hot air fr om the ducts inside within the house.

Thus, this means of heating has a capacity to pr ovide 5.56 kW dur ing a sunnyday, reducing the dependance on heat pumps, and indirectly reducing theelectr icity consumption.

ACTIVE HEATING AND COOLING :

Hot Air Solar Panels -

Domestic Hot Water -



SCHEMATIC DIAGRAM . . .



E n e r g y c o n s

u m p t i o n a n d g e n e r a t i o n

RENEW ABLE ENERGY

TECHNIQUES :

The r oof of the house ispitched at an angle of 8:12,pr oviding excellent solar exposure on the southernfaçade.

The PV gr id, in this case,consists of 26 solar panels of

190 Watt with an inverter f or 4.95 kW.

Cost of installation of PV was$1.50 / Watt as against the$7.50 / Watt rate because of the available state f inancialincentives to encourage NetZer o Homes.

The constr uction of the house was completed in the year 2008. The energyconsumption of the house was metered fr om January 1st , 2009 to January 1st ,

2010.Over the entire metered per iod the house generated 2.5 times as much energy asit used. The house has consistently had a surplus of energy of 1.5 times as muchenergy as it uses, sending a net surplus of 2,943 kWh back to the gr id.The energy used over the metered year was 1949 kWh and the energy pr oduced

using the PV array was 4892 kWh.

The actual perf or mance of the house exceeded the modeling. The house wasmodeled to have achieved a Net Zer o Annual with a PV system of 2kW. However,the installation of a 4.94 kW system made possible the better perf or mance of thehouse as against the simulated perf or mance.

ENERGY CONSUMPTION :



Annual Energy Balance : convert all site energy to kWh, then use Source multipliers to do the same for Source Energy.

Site Energy Source Energy

MBTUs MJ kWh MBTUs MJ kWh

Electricity (kWh) 1,949 6,558

Total Energy Consumed (kWh) 1,949 6,558

Renewable Energy MBTUs MJ kWh

Produced on site 4,892 16,462

Imported or derived from on-site processes

Purchased

Total Renewable Energy 4,892 16,462 16,462

Net Balance in kWh (Renewable Energy Provided-

Total Energy Consumed) -2,943 -9,903

US Residential Avg EUI: 44 MBTU/ft2 at site Site EUI 5.77 Source EUI 19.43

MBTU/ft2 MBTU/ft2

ENERGY BALANCE SPREADSHEET AND EUI FOR CONDITIONED AREA



C O S T A N D

M A I N T E N A N C E . . .

The total cost of constr uction f or the pr o ject was $180,000

The constr uction cost per square f oot was ± $156.25/sq.ft

This was slightly on the higher side, as the average cost of constr uction per sq. ftin Massachusetts is ar ound $125.92. However, with the generation of excesselectr icity using the PV array, 2943kWh electr icity was exported to the gr id. Thishelped to decrease the pay back per iod f or the expensive installations within thehouse.

COST OF CONSTRUCTION :

MAINTENANCE ISSUES :

The vent f or the Heat Recovery Ventilator posed a maintenance pr oblem.

Condensation occurs at a low temperature in the duct work, causing leakage over the insulation.

On the northern façade, not suff icient space is left between the cedar shingles onthe exter ior and the gr ound.

Also, the r oof overhang on the north side is less (few inches) as compared to theoverhang on all the other facades where it is appr oximately 2 ft.This has resulted in the gr owth of mildew posing a ser ious maintenance pr oblem

f or the occupants.

REFERENCES :

- Doug Stephens, owner and designer of the

Montague Ur banHomestead

- Zer o Net Energy Buildings: Residential Case Study.

- www.builditsolar .com

- http://www.nesea.org/inspirationawards/zeroenergy/20

10applicants/

- http://zechallenge.com/Step

hensClark-bio.htm

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Case Study Montague