Transcript
Pressure Balancing Chris Clay – The Building Performance Center Brad Turner – Southface
Objectives • Understand the problems pressure imbalances can cause in a home • Review basic pressure principles • Demonstrate pressure problems on a House of Pressure • Review the diagnostic tests used to identify and understand pressure problems • Learn different methods used to balance pressures in a home
Problems created by Pressure Imbalances • Infiltration / Exfiltration • IAQ issues – moisture, mold, odors • Increased energy use • Comfort issues
• Increased depressurization of CAZ • Back-drafting of combustion appliances • CO poisoning
Terminology • Pressure –
• A force encouraging flow by virtue of a difference in some condition between two areas. • The effect of a force applied to a surface • In Wx, usually measured in Pascals (Pa)
• Pressure Balancing –
• The process of neutralizing pressure differentials in the home • Performed by changing building components and/or mechanical systems to eliminate major pressure differences
Pressure Principles for Wx’ers • Airflow is measured in cubic feet per minute, also written as ft3/min, or CFM. • 1 CFM OUT = 1 CFM IN. • Airflow takes the path of least resistance. • Air moves from high- to low-pressure areas. • Air usually moves from high- to low-temperature areas.
Air Flow High pressure
Conditions for Air Movement • Pathways for air movement (hole) • Pressure difference (driving force)
Low pressure
Airflow Caused by Pressure Difference (P )
Positive
Negative
positive (high) to ______________ negative (low) pressure Flow is from ______________ enters one CFM _______ exits For every CFM that _______, least resistance Flow takes the path of _______
Types of Driving Forces Wind Heat: Stack effect, combustion Mechanical Systems and Fans: HVAC System, exhaust fans, duct leaks, interior doors
Stack Effect
Wind
Mechanical Systems
WIND DIRECTION
positive pressure
Wind creates a positive pressure on the windward side of the building . . .
negative pressure
Which creates a negative pressure on the other sides of the house
Stack Effect Warmer air rises and escapes out of the top of the house. . . Which creates a suction that pulls in outside air at the bottom of the house.
positive pressure Neutral pressure plane negative pressure
Stack Effect Positive pressure (with reference to outside)
Neutral pressure plane
Negative pressure (with reference to outside) Photo courtesy of David Keefe, Vermont Energy Investment Corp.
Combustion Equipment & Exhaust Fans
Negative pressure
Exhaust Fan
Negative pressure
Fans
Device
CFM
Bath
50
Range hood Downdraft hood “Chef” Hood
Mechanical Systems
150 500 1500
Dryer
200
Air Handler
400
/ ton
Duct Leakage Duct leakage can create positive and negative pressures in different areas of the house The pressures associated with duct leaks can be larger and more important because the driving force is stronger. All holes are not created equal!
Return
Supply
Duct Leakage Closed doors that prevent supply air from getting back to a return cause positive pressures in those rooms with supply vents. . . . Meanwhile, starving the return for air, causing negative pressure in the zone where the return is located.
Return
Supply
1616
Leaky Supply Ducts
Leaky Return Ducts
Room Pressure Imbalances Master Bedroom Utility Room
Kitchen
Whole-house return in hallway
Living Room Bedroom
Bath
Problems caused by Pressure Imbalances – Case Study
Dryer
DHW
HVAC R
Louvered Door
Dryer
DHW
HVAC R
Louvered Door
HVAC blower comes on; with doors closed and exhausts on, pressure imbalances occur
R
--
CO
CO
CO
+
+
+
+
CO
CO
Best approach is to use all sealed combustion appliances (or non-combustion appliances) Sealed Ductwork Comb. air w/ solid door
R
Solid, Weatherstripped Door, Insulated & Air Sealed Walls
Transfer Grilles Minimize Pressure Imbalances
Testing to determine pressure imbalances • • • •
Dominant Duct Leak Test All Doors Closed Test Room Pressure Test / Under Door Pressure Test Maximum Depressurization Test (Worst Case CAZ Depressurization)
Ensure a Proper Return Air Pathway: • • • •
Add return duct Install jumper ducts Install transfer grills Undercut doors
Plan your work
Jumper Duct
Transfer Grills
Transfer Grills
Return Air Pathway for Retrofits Tamarack Technologies, Inc. – www.tamtech.com
In-Door Pressure Balancer
Tamarack Technologies, Inc. – www.tamtech.com
Sizing return air pathway
Other fixes for pressure imbalances in CAZ • Down-size exhaust fan flows • Add ducted supply air to Combustion Appliance Zone • Shift supply air to different areas by adjusting HVAC system • Interlock supply air fan • Add supply air by bringing in outside air via dampered duct into return plenum
Pressure Balancing Process • Perform pre-test (test-in): This will give indications of what types of pressure balancing will be needed • Complete all air sealing and duct sealing work prior to pressure balancing • Perform interim testing • Install pressure balancing measures based on testing • Perform final test-out to verify success
Summary • Pressure imbalances can cause many problems in a home • Pressure imbalances are caused by many factors • Various diagnostic tests may used to identify and understand pressure problems • Several different methods are available for balancing pressures in a home
