1. Objectives Finish talking about ways to minimize ventilation losses Discuss role of ducts in building energy use Describe coheating test methodology Interpret duct retrofit results Measure duct leaks

2. Path Forward Read Chapter 1 of MCH for 3/2 Basics Read Chapter 2 for 3/7 Transport Read Chapter 3 for 3/21 Design Get errata from: http://www.buildingscience.com/updates/moisture _control_handbook_update.pdf http://www.buildingscience.com/updates/moisture _control_handbook_update.pdf MCH reading assignments – online version http://www.ornl.gov/roofs+walls/facts/index.html Incomplete (no Chapter 7, other differences)

3. Economizer Some buildings need cooling – even in winter Can get “free” cooling if outside air is below thermostat set-point Economizer = damper that lets in outside air Many commercial buildings (Seay Psychology building), some residential buildings

5. Economizer Issues Outdoor conditions Particularly humidity levels Control logic failures ~50- 60 % of commercial buildings have control problems Real world concerns Dampers stuck open/closed

6. Nighttime Flush Electricity is less-expensive at night Time-of-use pricing Lower electrical demand Fans use much less electricity than compressors Strategy: High ventilation rate overnight Large thermal mass accessible to air in building

7. Nighttime Flush Thermal Mass High density E = A∫q(t)dt Release energy next day Trombe wall/ rock wall for heating http://www.squ1.com/index.php?http://www.squ1.com/ passive/trombe-wall.htmlhttp://www.squ1.com/index.php?http://www.squ1.com/ passive/trombe-wall.html

8. Challenges for Nighttime Flush Radiation (comfort) Condensation Losses

9. Ducts Last major issue in ventilation Largely a US problem Swedish standard is 10,000 times stronger Largely a small building problem

10. Duct losses We (in the US) locate ducts outside of the conditioned space Duct losses account for 5-40% of the heating/cooling bill for the average American home Interaction between duct losses and indoor air quality? Some ducts are under negative pressure

11. Duct locations Attic Crawlspace Garage Interior soffits Basements Floor joists

13. Duct terminology Supply and return ducts Operating pressure Leakage to inside and outside Air handler flow

14. Duct efficiency System efficiency Penalty associated with duct system Conduction losses (β) Leakage losses (α) Infiltration interaction Heat delivery efficiency HDE = energy out of registers/energy in at furnace ASHRAE Standard 152 Calculation and measurement protocol

15. http://oikos.com/esb/28/duct_losses.html

16. How do we measure duct efficiency? Short term coheat tests Heat house normally with furnace + ducts Maintain same temperature distribution with space heaters Monitor total power consumed by house η sys = P heaters / P furnace

18. Coheat challenges Only one group has done them on a large scale and successfully Very expensive and labor-intensive Doesn’t work for cooling (why not?) Attempted in Florida in 1999-2000

19. Because of challenges with coheating, Most conservation programs focus on duct leakage Sealing addresses leakage and infiltration losses Duct efficiency  leakage losses Need an accurate way of measuring leakage

20. Duct leakage Subtraction Duct pressurization Nulling test Delta-Q

21. Blower door subtraction Can use blower door Measure building leakage with registers sealed and unsealed Difference is duct leakage Problems?

22. Duct pressurization Seal registers and pressurize ducts (like blower door testing) Add blower door to eliminate pressure difference between ducts and building Leakage to outside Problems?

23. Duct leakage Ref: Siegel et al. (2003)

24. Air handler flow Duct efficiency scales with fraction of flow that is leaked to the outside (α) Typically, we measure duct leakage flow, so, in order to get α Need air handler flow Several approaches Replace air handler fan with calibrated fan and match pressure distribution Hot-wire anemometer traverse Temperature rise method q = mCΔT Measure q, ΔT and calculate m

25. Nulling test Use blower door or duct blaster Zero out pressure difference caused by unbalanced leakage Seal off return side of system measure supply leakage directly Directly measures leakage flows at operating pressures Ref: Francisco and Palmiter (2000) ASHRAE Transactions

26. Unbalanced Leakage Q s -Q r

27. Delta-Q test Measure the pressure/flow response of house With air handler on With air handler off Use software and power-law relationship to get duct leakage to outside Requires complicated model Accuracy still being debated Walker et al. (2001)

28. Other ideas Flow plate w/ flow hood

29. How do you seal leaks? http://www.wisconsinpublicservice.com/business/art/EA39_1.jpg

30. Duct mastic

31. Why no duct tape? http://www.tence.net/people/images/duct-tape.jpg http://www.homeenergy.org/898ducta pe.title.html http://ducts.lbl.gov

33. System Efficiency

34. Percentage reduction in space heating energy requirements

35. The morals of the story Duct leakage is important Measuring it accurately is difficult Several approaches are available Active area of research