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100% Outside Air and Dehumidification Management
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  1. 100% Outside Air and Dehumidification Management

  2. 100% Outside Air - What is it ? • Referred to as “Make-up Air” • Unit operates continually during occupied mode • Replaces exhausted air • No mixture with return air • Totally changing load • Summer design (High temperature and high humidity) • Winter design (Cold temperature)

  3. Why 100% Outside Air? • Ventilation standards indicating recommended air changes for a variety of space usages and occupancy have been established by ASHRAE. The ventilation requirements for a given structure or space are based either on desired number of air changes or the number of occupants. • The amount of outside air fresh air required for each change per hour equals the amount of inside air that must be removed from the space during the same time span. • CFM= Area of space / Minutes of air changes

  4. Ventilation Requirements (continued) • College classroom 8 air changes 20-30 cfm/person • Hospitals 9-17 air changes 40-50 cfm/person • Kitchens 10-20 air changes 40-50 cfm/person • Schools 8-12 air changes 30-35 cfm/person • Theaters 5-10 air changes 10-15 cfm/person • Factory Buildings 10-15 air changes 25-30 cfm/person

  5. Return Air Ducts Typically will not affect space conditions May not require Reheat Control is not as critical Direct to Space Usually applied to large areas (Auditoriums, Kitchens, Corridors) More precise control is necessary Reheat is required for control Applications of Make-Up Air

  6. 100% Outside Air “Supply Air Properties” • Unit discharge air properties • Main purpose – positively impact building humidity • Lowest dew point possible • Ideally close to room (neutral) conditions • Typically between 68 -72 degrees • Not to overcool or overheat space • Below 70% RH per ASHRAE standards

  7. Dew Point Comparison Reheating to Neutral Air

  8. Air Control • Leaving Air Control • Hot Gas Reheat • Cycling Control • Modulating Control • Room Control • Hot Gas Reheat • Cycling in conjunction with a reheat thermostat • Modulating in conjunction with a reheat sensor

  9. 100 % Outside Air - Room Reheat Control T Reheat Control - room thermostat in series with discharge thermostat (neutral or cold air) T

  10. Single Compressor -- Single Circuit Used when low dew point in required Dehumidifies all the air all of the time Dual Circuits – Single Compress each circuit Used when leaving air conditions are not critical Air will bypass lag circuit and then mix with lead circuit Dual Circuits – Two compressors (Tandem) each circuit) Lag compressor cycles based on suction pressure. Four (4) stage operation Large Tonnage Compressors Usage

  11. Hot Gas Bypass Modulates to match the evaporator load Evaporator freeze protection Suction pressure activated Hot Gas Reheat Raises leaving air temperature to room neutral conditions Cycling with discharge air thermostat Modulating with sensor. Liquid Subcool Coil Raises leaving air temperature Subcools liquid Two (2) degrees of subcool equals one (1) percent increase in evaporator capacity “Refrigeration” Control

  12. Standard Cycling Hot Gas Reheat

  13. Hot Gas Reheat Plus Sub-Cooling

  14. Hot Gas Reheat Using Digital Scroll

  15. 100% Outside Air Example • Summer design • 1800 cfm • 92/75 ambient • Leaving air • 55 deg Dew Point • 65 deg leaving air temperature • Winter design • 0 degree ambient • Leaving air (minimum 70 deg)

  16. 100% Outside Air Summer Design w/Reheat Supply Temp. 55.0/55.0 Ambient 92/75 Leaving Air 79.7/64.1 10 ton 1800 cfm

  17. 100% Outside Air Summer Design w/Reheat Plus Liq. Sub-cool 66.1/59.4 Supply Temp. 52.2 D.P. Ambient 92/75 10 ton 1800 cfm Leaving Air 90.5/67.7

  18. 100% Outside Air Summer Part Load w/Reheat Supply Temp. 53.9 D.P. Ambient 75/75 Leaving Air 86.1/64.3 10 ton 1800 cfm

  19. 100% Outside AirPart Load w/Reheat Plus Liq. Sub-cool 65.7/58.8 Supply Temp. 50.8 D.P. Ambient 75/75 Leaving Air 94.0/67.1 10 ton 1800 cfm

  20. 100% Outside AirSummer Part Load w/Reheat Supply Temp. 48.8/48.8 Ambient 70/70 Leaving Air 79.5/61.2 10 ton 1800 cfm

  21. 100% Outside AirPart Load w/Reheat Plus Liq. Sub-cool 59.9/54.3 Supply Temp. 48.1 D.P. Ambient 70/70 Leaving Air 83.1/64.3 10 ton 1800 cfm

  22. 100% Outside AirSummer Part Load w/Reheat Supply Temp. 46.8/46.8 Ambient 65/65 Leaving Air 73.7/63.8 10 ton 1800 cfm

  23. 100% Outside AirPart Load w/Reheat Plus Liq. Sub-cool 55.8/51.5 Supply Temp. 47.0 D.P. Ambient 65/65 10 ton 1800 cfm Leaving Air 79.4/61.0

  24. 100% Outside AirSummer Part Load w/Reheat Supply Temp. 51.4/51.4 Ambient 60/60 Leaving Air 64.3/56.2 10 ton 1800cfm

  25. 100% Outside AirPart Load w/Reheat Plus Liq. Sub-cool 55.2/52.1 Supply Temp. 50.4 D.P. Ambient 60/60 Leaving Air 72.6/57.4 10 ton 1800 cfm

  26. 100% Outside AirWinter Design Conditions 175,000 BTUH Furnace Ambient 0 Leaving Air 72 10 ton 1800 cfm

  27. Do No Harm Dehumidify to 55 0 Dew Point or less. Reheat to Room Neutral. Temper to Room Neutral Possible humidify when ambient temperatures are below 35 0 Recap

  28. Energy Conservation Wheel Applications • Require exhaust air from the building • Require defrost in most areas • Total Unit EER can exceed 25 on some water source heat pump applications

  29. Dedicated Outdoor Air Load Reduction Example: Loads based on: • 4250 cfm supply and exhaust airflow • 48” Energy Conservation Wheel • 75F/ 50%RH summer exhaust air • 70F / 30%RH winter exhaust • Source: www.novelaire.com (graphic)

  30. for your attention