Announcements Midterm Project Prepare groups of 3 to 4 students You can submit the list at the end of next class Midterm Exam 03/09/10 - In class Exam: 75 min be earlier in the classroom - Example exam posted on the course website next class: review

Air Handling Units (AHS) Equipment For AHU: Fans Cooling and heating coils Combustion heat exchangers Filtration Dampers, controls, mixing valves Humidification: steam/spray Dehumidification: cooling coil/desiccant Noise control

Air Handling Unit (AHU) Compressor and Condenser Roof top AHU Gas/Electric Heater to building Fan air from building fresh air Evaporator filter mixing hot water cool water Return fan Supply fan flow control dampers AHU Fresh air AHU schematic Outdoor air To room ExhaustFrom room

Control of air Systems Vary temperature, constant flow Constant temperature, vary flow Vary temperature, vary flow

How does a residential thermostat work? A.Calculates difference between actual temperature and required temperature and adjusts furnace/AC output accordingly B.Measures temperature continuously and turns equipment on and off when temperature is different from set point temperature C.Measures temperature continuously and turns equipment on and off when temperature is outside of specified bounds D.Calculates difference between actual temperature and required temperature and adjusts the velocity of the fan (flow-rate) accordingly

Constant Temperature, Variable Volume On-off systems Residential and small commercial Vary volume by turning system on and off

Constant Air Volume Single zone constant air volume Fan always runs Vary temperature of air in response to space thermostat Single zone constant air volume with reheat Often used for precise humidity control Multizone constant air volume with reheat Good humidity control, flexible Not very efficient

Constant Volume – temperature control Proportional control or Proportional Integral control Thermostat measure: ΔT = T set point – T zone air Send the signal to the valve of cooling/heating coil

Multizone constant air volume with reheat 55°F 62°F55°F Require less cooling

Variable Air Volume Single zone VAV Varies air flow based on room thermostat Multizone VAV Central chilled air supply Zone thermostats control flow to each zone Can also use reheat Still need to provide adequate air flow for ventilation and for comfort Smaller energy penalty than CAV

VAV terminal

Multizone VAV 55°F Vary the flow

Dual-Duct Systems Can be VAV or CAV Two plenums with chilled air and heated air Zone thermostats control ratio Separate duct for each zone

Summary of Air systems Choice between air systems determined by: Possibility/desirability of reheat Energy efficiency Importance of humidity control Availability of waste heat Building size

Water systems Fan coil Fan terminal unit Baseboard heaters Radiant panels, chilled beams Two pipe or four pipe water system

or cooling

chilled beams Radiant panel Radiant panels

Reading Assignment Tao and Janis Chapter 3 Sections: (including ) Chapter 6 (from 6.1 to 6.7)

Homework Assignment 4 Table 1 Results of cooling load calculation and required amount of fresh air for ventilation Zone 1 Zone 2Zone 3Whole building Sensible cooling load for zone Time when the max cooling load appear Btu/h at 4 PM Btu/h at 6 PM Btu/h at 8 AM Btu/h at 6 PM Sensible cooling load for critical hour for whole building (6 PM) Btu/h at 6 PM Btu/h at 6 PM 9000 Btu/h at 6 PM Latent cooling load (internal sources + infiltration) 5400 Btu/h5200 Btu/h5400 Btu/h16000 Btu/h Required amount of fresh air based on number of occupants 240 CFM (12 occupants) 520 CFM (26 occupants) 240 CFM (12 occupants) 1000 CFM (50 occupants)

Homework Assignment 4 Supply air 55°F Recirculation air 76°F Fresh air (Dallas, TX) DBT=102°F