Zonal Pressurization Diagnostics (ZPD) Matt Sharpe, Vermont Energy Investment Corporation Loose Presentation Outline Air flow fundamentals How to exploit these basic principles (i.e., zonal pressure diagnostics) Some Quick & Dirty tips Some examples Lots audience participation Air Flow Fundamentals Air is LAZY It will only go where it is forced to go Air requires 2 things for it to flow for it to be an air LEAK 1. A hole a path for the air to flow through 2. A force - a pressure difference between one side of the hole and the other If you know 1 & 2 above Air Flow can be calculated:
Stack Effect Remember that temperature differences create pressure differences The greater the temperature difference, the greater the pressure difference Air Flow carries stuff with it like: Heat energy Moisture Other pollutants More Fundamentals - Units Measured Flow is in cubic feet per minute (cfm) Pressure differential is in pascals (pa), or in water column inches ( w.c.) 1 Pascal = 0.004 inches water column ( w.c.); (248 pa = 1 w.c.) (25 pa = 0.1 w.c.) Cfm50 means cubic feet per minute at a 50 pascals pressure difference
Tools for Measuring Pressure Differences Things to keep in mind when taking measurements? Measure pressure differences between one space and another - NOT total pressure Always have to be aware of what space is at issue with respect to (WRT) what other space Double check your test results: Zone WRT outside (a) + Zone WRT inside (b) = inside WRT outside (c) What Information Are We After? Are these two zones connected? How much leakage exists to the zone (attic/basement/crawlspace/garage)? How much reduction in house CFM50 can we get by sealing this area? Is it worth cutting into this space? Did we do a good job of sealing this barrier?
Two Ways of Inducing Pressure Differentials 1. With house or ducts Depressurized or Pressurized with Test Equipment Blower door Duct Blaster 2. Using Existing Equipment in Building Air Handler Exhaust Fans Combustion Appliance
FIRST! Measure Baseline Pressure Differences Prepare as if doing a blower door test (fans off, windows closed, etc.) House WRT Outside Hose ending up outside, connected to manometer inside Take a baseline reading or zero gauge Zone WRT House Hose ending up in zone (not pinched), connected to manometer inside Take a baseline reading or zero gauge Diagnostics using Test Equipment Measure Baselines Use blower door to create a measured pressure difference between house and outside (usually 50 pa) and make note of cfm@50 value Measure Zonal Pressure Differential Pressure tap in attached garage WRT house Attic or crawl space WRT house From room to room Between ducts and house (with registers sealed)
Is that bad? If you want the zone to be inside (an interior wall) then you want 0 pressure difference between the zone and inside. If you want the zone to be outside (an attic) then you want as big a pressure difference to the zone as you have to the outside (50 pa) Usually you will be somewhere in between House a -50 pa using blower door Tight ceiling, negative pressure Leaky ceiling, same conditions (50 pa) in house WRT outside Holes in ceiling cause pressure If attic is outside then house drop in house WRT attic value WRT attic should be 50 pa (and attic WRT outside 0 pa) What does it mean if the House WRT Attic zone is 37 pa while the House WRT to outside is 50 pa? Is the attic more outside than inside? Are there holes between the house and the attic? Are there holes between the attic and outside? What do we do with this number? The are several ways to analyze it, but first Write it down you ll need it again when you test-out!
Pressures and Leakage Zone Pressures House-Zone Zone-Out 12 38 25 25 37 13 41 9 45 5 48 2 49 1 Relative Size of Leaks House-Zone Zone-Out 2 1 1 1 ½ 1 1/3 1 ¼ 1 1/8 1 1/13 1 Take the test an extra step to estimate cfm@50 leakage rate into zone You already know: house cfm50, pressure differential in zone WRT house Next step: Add a Hole Turn up blower door to get back up to 50 pa Measure: Cfm50 and pressure differential in zone WRT house Cox/Olson charts Beginning house to zone = 37 pa w/ added hole house to zone = 18 pa Multiplier = 1.26 Beginning house cfm50 = 2500 w/hole = 3200cfm Cfm50 diff = 700 700*1.26 = 882 cfm
Remeasuring When You Think You re Done Outside zones (attic, garage) should be much closer to 50 than when you started Inside zones (interior walls, chases, ducts) should be much closer to zero than when you started Zones that haven t changed much in the right direction are opportunities for further improvement
Limitations/Cautions Don t attribute much meaning to measurements between 47 & 50 Small errors in measuring may generate large errors in the result Don t assume attic is OK because pressure is 48 Can seal zone-exterior (attic vents) to get numbers into a better range Limitations/Cautions Testing zones that are connected and adding the results will overstate the leaks (counts the connecting leaks twice) Need to identify them as interconnected Identifying Interconnection Depressurize house to 50 Pa Measure pressure to 1st zone Open a door to the 2nd zone, readjust blower door to read 50 Pa If the zones are connected, the pressure in the first zone will change, If not, it won t
Limitations/Cautions Be sure to account for baseline pressures Re-check unusual measurements If a number is unbelievable, don t believe it! Disconnected, misplaced or pinched hoses Unknown fans Mis-read gauges Diagnostics using Equipment in Building Use Exhaust Fans and a calibrated pressure pan to measure fan flow in cfm Use Exhaust fans (bath fans, dryer, range hood) and air handler to identify Worst Case depressurization of the Combustion Appliance Zones (CAZ) With CAZ at worst case; test Backdrafting potential Use Air Handler Fan to identify Dominant Duct Leakage Use Door Closure to identify pressure imbalances
Cfm = 1.07, times square root of pressure differential, times square inches of hole area Another handy tool: A calibrated hole Exhaust Fan Flow Meter TM *If Pressure difference more than 8pa move slide gate to next largest opening Measure Exhaust Fan Flow (Home made Flow Box) 1.07 x (square root of Pascals) x (square inches) = cfm 9.0 2 Square root of 9 pascals = 3 4 x 2 = 8 square inches 4 SO: 1.07 x (3) x (8) = 25.68 cfm adapted from Anthony Cox
Thank you! Matt Sharpe msharpe@veic.org Vermont Energy Investment Corporation www.veic.org Efficiency Vermont www.efficiencyvermont.com