Pressure Balancing. Chris Clay The Building Performance Center Brad Turner Southface

Transcription

1 Pressure Balancing Chris Clay The Building Performance Center Brad Turner Southface

2 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

3 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

4 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

5 Pressure Principles for Wx ers Airflow is measured in cubic feet per minute, also written as ft 3 /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.

6 Air Flow High pressure Low pressure Conditions for Air Movement Pathways for air movement (hole) Pressure difference (driving force)

7 Airflow Caused by Pressure Difference ( P ) Positive Negative Flow is from positive (high) to negative (low) pressure For every CFM that, enters one CFM exits Flow takes the path of least resistance

8 Types of Driving Forces Wind Heat: Stack effect, combustion Mechanical Systems and Fans: HVAC System, exhaust fans, duct leaks, interior doors

9 Stack Effect Wind Mechanical Systems

10 WIND DIRECTION positive pressure negative pressure Wind creates a positive pressure on the windward side of the building... Which creates a negative pressure on the other sides of the house

11 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 negative pressure Neutral pressure plane

12 Stack Effect Positive pressure (with reference to outside) Neutral pressure plane Photo courtesy of David Keefe, Vermont Energy Investment Corp. Negative pressure (with reference to outside)

13 Combustion Equipment & Exhaust Fans Negative pressure Exhaust Fan Negative pressure

14 Fans Device Bath CFM 50 Mechanical Systems Range hood Downdraft hood Chef Hood Dryer Air Handler / ton

15 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

16 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 16 16

17 Leaky Supply Ducts

18 Leaky Return Ducts

19 Room Pressure Imbalances Master Bedroom Utility Room Kitchen Whole-house return in hallway Living Room Bedroom Bath

20 Problems caused by Pressure Imbalances Case Study Dryer DHW HVAC R Louvered Door

21 Dryer DHW HVAC R Louvered Door

22 HVAC blower comes on; with doors closed and exhausts on, pressure imbalances occur CO CO CO R - CO + + CO

23 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

24 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)

25 Ensure a Proper Return Air Pathway: Add return duct Install jumper ducts Install transfer grills Undercut doors

26 Plan your work

27 Jumper Duct

28 Transfer Grills

29 Transfer Grills Return Air Pathway for Retrofits Tamarack Technologies, Inc.

30 In-Door Pressure Balancer Tamarack Technologies, Inc.

31 Sizing return air pathway

32 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

33 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

34 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