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Kitchen Exhaust Ventilation with HRV at Ankeny Row

Case Study by Dylan Lamar, Green Hammer and Tad Everhart, Energy Advisor LLC
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Kitchen Exhaust Ventilation with HRV at Ankeny Row
Energy
Heating, Ventilation & AC
Ventilation
Continuous kitchen ventilation with heat recovery
Portland
9956
Jody Orrison, Administrative Appeal Board
Green Hammer
Residential
1400
Green Hammer
Green Hammer
Earth Advantage Home Certification - Platinum Level and Earth Advantage Net Zero Energy

Abstract

Green Hammer’s Ankeny Row homes meet the Passive House Standard with whole-house, balanced, continuous ventilation with heat recovery.  This ventilation system includes an exhaust vent located in the kitchen. Code requires a direct-through-envelope, intermittent operation, high-volume range hood exhaust system.  On appeal, Green Hammer demonstrated the passive house ventilation system is environmentally superior because it provides more ventilation than the code requires as well as heat recovery for greater energy efficiency.  The City of Portland allowed this ventilation system as “an alternate method/material.”

Permitting Process

The building code requires direct, through-wall/roof, high-volume kitchen ventilation.  This ventilation requirement would result in significant heat loss, which is inconsistent with our passive house ventilation system and makes it difficult to meet the passive house airtightness requirement.  We filed a written code appeal including our reasons for and evidence in support of our alternative ventilation system with the building official and obtained approval of our kitchen ventilation system as an alternative means of providing code-required kitchen ventilation.  We demonstrated that our system would provide more ventilation than the code required, it was safe, and it was environmentally superior.

Code RequirementCompliance Path
2011 ORSC section M1503.4 Domestic kitchen cooking appliances shall be equipped with a ducted range hood Architect/builder submitted written building code appeal with supporting information and fee.  Administrative hearing decided by City staff who posted written approval online (see appeal item 3)
2011 ORSC section M1503.1 Range hoods shall discharge to the outdoors through a single-wall duct.

Project Summary

Ankeny Row HRV

The building code requires direct, through-wall/roof, high-volume kitchen ventilation (at least 150 cfm intermittently).  This ventilation requirement makes it difficult or impossible to meet the passive house airtightness requirement.  It adds considerable expense because a passive house is virtually airtight.  To exhaust 150 cfm from an airtight building, you need make-up air from outdoors.  Moving 150 cft of air from outdoors causes drafts and unwanted heat loss/gain.  Even when not in operation, in order to prevent unwanted heat transfer, you need air-tight dampers for both the exhaust duct and make-up air duct.  And direct exhaust  prevents recovery of heat from the exhaust air in winter.HRV diagram

We demonstrated that our kitchen ventilation with heat recovery system would provide more ventilation each day than the code-required kitchen ventilation system, it was as safe, and it allowed better energy efficiency and thermal performance.  Our system eliminated unnecessary holes in the air-tightness layer of the walls, and allowed heat recovery.  The building official granted our appeal and allowed our kitchen ventilation system.

Resources

Passive House Northwest Website Heriott Watt University Technical Report on Drainage Waste and Vent Systems Green Hammer page on Passive House

Project Details

Green Hammer designed the homes in Ankeny Row to include whole-house, mechanical ventilation with balanced flow of air from the outdoors into the house and air exhausted from the house to the outdoors.  The ventilation system includes heat recovery (HRV).  The ventilation system exhausts air from areas with sources of contamination (including moisture): kitchen, bathrooms, and laundry.  Each kitchen includes an exhaust vent through which the HRV continuously pulls at least 25 to 35 cfm of stale air and exhausts it to the outdoors.  The HRV transfers approximately 90% of the heat from the exhaust air to the incoming cooler air to reduce the “ventilation energy penalty.” In addition, each kitchen includes a range hood which circulates air through filters to remove odors and prevent contamination of the ventilation system

Green Hammer calculated its proposed kitchen exhaust system provided a continuous exhaust rate of 25-35 cfm to exhaust in 24 hours nearly five times as much air as the entire house contains.  A code-equivalent exhaust system with not only a range hood, but also bathroom fans and clothes dryers exhausting air for one hour per day would result in only one house full of air exchanged in a 24 hour period. (see calculations in Related Documents)

The 2011 ORSC section R104.11 allows “Alternative materials, design and methods of construction and equipment” when such “material or work offered is, for the purpose intended, at last the equivalent of that prescribed in this code in quality, strength, effectiveness, fire resistance, durability, and safety.”   There was only one step in the appeal process: submitting the appeal (along with others needed for the project as designed) in writing  on the form supplied by the City of Portland along with the $227 fee.  The building official granted the appeal in an administrative hearing decided by City staff.  Applicants are not invited to attend unless their application is initially denied.

The proposed ventilation was not just equivalent to what the 2011 ORSC required, but it exceeded the code required ventilation.
Also, Green Hammer pointed out several Passivhaus projects locally and accounts from many such projects throughout the US and Europe confirming the safety, superior indoor air quality attained, and functionality of the proposed ventilation system.

Design / Build Process

Green Hammer designed and constructed six attached single family residences in a community called Ankeny Row (on SE Ankeny Street).  Green Hammer worked with the homeowners for several months refining the design of the homes to meet the homeowners’ goal of net zero energy, low-environmental impact, durable homes built with sustainable materials.  Green Hammer supports all of these goals, and it carefully designed the homes to be a net zero energy energy annually (producing as much electricity onsite with rooftop solar PV as the homeowners consume in their homes each year).  In order to reach this goal, energy-efficiency guided every step of design and construction.  Thus, all of the homes approach or meet the Passive House Standard, the world’s most rigorous building operating energy efficiency standard that strictly limits air leakage, energy use for space heating and cooling, and whole-building annual operating energy.  A passive house must be airtight, (leakage < 0.6 ACH @ 50 Pa), so a hole in the house for direct-through-envelope, ducted, 150 cfm exhaust causes many problems, i.e. substatial heat loss from a duct and damper used only intermittently for short periods of time.  It would require a dedicated source of make-up air, likely requiring another large hole, damper, incidental leakage, etc.).  Conventional, through-wall or through-roof kitchen vents add costs, complexity, and potential maintenance, repair, and replacement obligations, while exhausting relatively warm air and introducing relatively cold make-up air into the home in winter.  The huge energy penalty makes it difficult to meet both net zero energy and passive house goals.  Recycling the heat produced from cooking with heat recovery ventilation helps reduce the space heating load. (cost benefit?)   By employing “passive” heating strategies such as recycling heat from air exhausted from the home by the ventilation system, a micro heater is sufficient for the tiny space heating load.  In fact, Green Hammer’s energy modeling shows that these six homes have an average peak heating load of 1,500 watts--the output of a small hairdryer; and a load easily met with the rooftop solar PV electricity generation.

Cost/Benefit

There was no additional material or labor cost since Green Hammer had always planned to install all of the components of the heat recovery ventilation system.  Not only are the Ankeny Row first-costs (design and construction) lower than the code-required alternative, but Green Hammer expects the Ankeny Row houses will experience the tremendous operating energy savings that buildings meeting the Passive House Standard enjoy year after year.  These savings greatly exceed the incremental additional costs for premium building materials and superior quality construction required to meet the Standard.  In fact, with their rooftop solar PV arrays supplying all operating electricity, the Ankeny Row houses will have no operating energy bills.

Project Contacts
Designer: Dylan Lamar, Certified Passive House Consultant Green Hammer (503) 804-1746 Approving Offcial: Jody Orrison, Administrative Appeal Board City of Portland Bureau of Development Services (503) 823-7526
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