Variable Air Volume with Indoor Air Quality

Transcription

1 Variable Air Volume with Indoor Air Quality and a Cure for the Spread of the Airborne Flu Virus January 11, 2017 Dinner Meeting Golden Gate ASHRAE Chapter Presented By: Thomas S. Weaver, P.E., Member ASHRAE

2 Special Thanks Mike Scofield P.E., Fellow ASHRAE Dr. Nicholas Des Champs, PhD, P.E., Fellow ASHRAE Dr. Stephanie Taylor, MD, M ACH, William J. Fisk, Staff Scientist, LBNL Sara Cantrell, Graphic Design

3 Learning Objectives 1. Understand how the maintenance of indoor Relative Humidity (RH) above 40% will reduce the spread of airborne Flu virus in the human breathing zone during a California winter.

4 Learning Objectives 1. Understand how the maintenance of indoor Relative Humidity (RH) above 40% will reduce the spread of airborne Flu virus in the human breathing zone during a California winter. 2. Understand how an HVAC design using a Heat Recovery Economizer (HRE) for a Variable Air Volume (VAV) overhead delivery system can provide 100% outdoor air in California during cold ambient conditions.

5 Learning Objectives 1. Understand how the maintenance of indoor Relative Humidity (RH) above 40% will reduce the spread of airborne Flu virus in the human breathing zone during a California winter. 2. Understand how an HVAC design using a Heat Recovery Economizer (HRE) for a Variable Air Volume (VAV) overhead delivery system can provide 100% outdoor air in California during cold ambient conditions. 3. Understand how an adiabatic Direct Evaporative Cooler/Humidifier (DEC/H) component in an Air Handling Unit (AHU) can, in California, provide free humidification with 100% outdoor air during dry winter ambient conditions.

6 Important Acronyms RH - Relative Humidity VAV - Variable Air Volume HRE - Heat Recovery Economizer DEC/H - Direct Evaporative Cooler/Humidifier AHU - Air Handling Unit ACH - Air Changes per Hour IAQ - Indoor Air Quality HAI - Hospital Acquired Infections IEC - Indirect Evaporative Cooling WBDE - Wet Bulb Depression Efficiency WB - Wet Bulb (Temperature) DB - Dry Bulb (Temperature) ADPI - Air Diffusion Performance Index EER - Energy Efficiency Ratio (Cooling Btuh/watts) OA Outdoor Air EA Exhaust Air

7 Summary Part I What we know that is key to the spread of airborne pathogens (as it applies to indoor RH) Part II Improving IAQ (reducing the spread of air born pathogens) through applying HRE combined with VAV while meeting code and saving energy Part III Other OA benefits

8 Part I The Spread of Airborne Pathogens Transmission of Infections is Dependent on 6 Factors: 1. The number of people producing infectious droplets 2. The vulnerability of people 3. The length of the occupant s exposure 4. The ventilation rate 5. The settling rate of infectious droplets 6. The survival of pathogens in droplets during transmission

9 Part I The Spread of Airborne Pathogens Which of these 6 are influenced by RH? 1. The number of people producing infectious droplets 2. The vulnerability of people 3. The length of the occupant s exposure 4. The ventilation rate 5. The settling rate of infectious aerosols 6. The survival of pathogens in aerosols during transmission

10 Part I The Spread of Airborne Pathogens Don forget your sweater or you will catch a cold.

11 Part I The Spread of Airborne Pathogens Moisture content (RH) may, indeed, be the most important environmental factor influencing the survival of airborne microbes. R. L. Dimmick, Naval Biological Laboratory, Univ. CA, Berkeley, Circa 1966

12 Part I The Spread of Airborne Pathogens Indoor relative humidity (RH) contributes to the buoyancy and viability of airborne pathogens. Air turbulence in the human breathing zone. The combination of low RH and turbulence in the human breathing zone.

13 Thermodynamics of Infectious Droplets at 20% RH HUMAN AIR: F 95% RH DRY ROOM AIR: C 20% RH H 2 O ENERGY AND MASS TRANSFER Evaporation / Condensation KINETIC MOVEMENT Thermal Buoyancy ❶ Expulsion Natural or Forced Convection Heat Transfer Force of Gravity Resultant Trajectory

14 Part I The Spread of Airborne Pathogens At 20% Indoor RH-Dry

15 Thermodynamics of Infectious Droplets at 50% RH HUMAN AIR: F 95% RH HUMIDIFIED ROOM AIR: F 50% RH H 2 O ENERGY AND MASS TRANSFER Evaporation / Condensation KINETIC MOVEMENT Thermal Buoyancy ❶ Expulsion Natural or Forced Convection Heat Transfer Force of Gravity Resultant Trajectory

16 Part I The Spread of Airborne Pathogens At 50% Indoor RH Humidified

17 Part I The Spread of Airborne Pathogens Disinfection is More Effective 40-60% indoor RH: infectious droplets settle nearby Allowing surface cleaning to work!

18 Part I The Spread of Airborne Pathogens We Need to Maintain Maximum AND Minimum RH!

19 Part II Improving IAQ One solution to indoor pollution, and the spread of airborne pathogens is dilution (100% OA) More energy to condition outdoor air Heating, cooling and humidification or dehumidification Increase ventilation through increasing air change rates Higher fan energy More noise from fan systems Increased energy for heating or cooling the air

20 Part II Improving IAQ Important Studies If we reduce ACH from 6 to 2, it is a (combined) 70% energy savings on HVAC reheat and fan energy during ambient conditions when airside economizes are used Study The Natural Experiment in California Hospital Ventilation Rates by English, Castillo, Darwich.

21 Part II Improving IAQ Important Studies VAV terminals may be set as low as 10% (90% turn down) without compromising comfort for people. In fact they had less cold complaints. The research shows savings of 10% to 30%. ASHRAE Research Project 1515, Arens E., et al. 2015

22 Part II Improving IAQ Important Studies Use of high air diffusion performance index (ADPI) for better room mixing and to avoid dumping of low temperature air at low diffuser flows. ASHRAE s Cold Air Distribution System Design Guide

23 Part II Improving IAQ Question How can we meet minimum ventilation rates, optimize RH, improve IAQ, improve the health of the occupants and save a significant amount of energy?

24 Part II Improving IAQ Here is How: West Coast VAV Fresh Air Design

25 Part II Improving IAQ Sacramento, CA Performance-Summer

26 Part II Improving IAQ

27 Part II Improving IAQ

28 Part II Improving IAQ The 100% OA evaporative cooling design reduces the mechanical cooling peak energy demand by 76.6% (while introducing 100% outdoor!) A total of 22,119 ton-hours per year savings for the 10,000 CFM VAV system when compared to a 25% minimum OA economizer design

29 Part II Improving IAQ

30 Part II Improving IAQ Important to note that, in the winter, 27% of the annual hours occur between 62 and 57 degrees F when only the DEC/H (12 wetted media pad) is required to meet set point. The cooling efficiency ratios (EER) approaching 100 are possible. The marriage of a VAV fan system to an IDEC improves the performance of the IEC components as the flow drops to meet the lower demand thereby increasing effectiveness

31 Part II Improving IAQ

32 Part III Other Benefits Other Outdoor Air Benefits Free Humidification Office worker productivity increases Short-term sick leave reductions Air Filtration Sound performance

33 Part III Other Benefits

34 Part III Other Benefits From an ASHRAE presentation How Indoor Environments Affect Health and Productivity the continuous increase in OA (from 15 CFM to 106 CFM per person) a 4% increase in productivity could be achieved resulting in huge savings for companies.

35 Part III Other Benefits

36 Part III Other Benefits Another study shows that an increase in OA ventilation from 24 CFM to 48 CFM per person results in a 33% reduction in short term sick leave rates. Short-term sick leave in schools is tied to funding. A 33% reduction in student absente rates would have major impact on school budgets.

37 Part III Other Benefits

38 Part III Other Benefits The DEC can serve as backup filtration. Based on ASHRAE Standard and a face velocity of 500 feet per minute the DEC has a particle removal efficiency of 16%. The DEC will remove more than 90% of airborne particles larger than 10 micron from the outdoor air.

39 Part III Other Benefits

40 Conclusion If we can design a VAV supply air system that provides indoor humidity control and delivers more CFM of outdoor air than prescribed in Standard 62.1 with energy savings why not do it?

41 Again Thank you Q & A