Important variables Water: Air: Conversion: - Use ASHRAE tables I gave you: - You can fine them online http://www.engineeringtoolbox.com/unit-converter-d_185.html (be careful, not all online converters are correct)

Objective Finish cooling & energy storage systems Define Building Zones Learn about air handling and water distribution systems

Absorption Cycle Water is typical refrigerant Strong vacuum - ~0.116 psi or 0.0008 MPa Boiling point of water? Differences from vapor compression No compressor Chemical (e.g. LiBr - hygroscopic) Absorbs water vapor turns it into a liquid Regenerated by removing water Requires heat

Absorption Cycle Strong vacuum Refrigerant: water Absorber: lithium bromide Replace compressor

Evaporative Cooling Wet media/water spray – direct Raise absolute humidity, lowers temperature of conditioned air Cooling tower – indirect Cools through a heat exchanger Lowers temperature, does not affect absolute humidity Can directly cool air in cold weather

Evaporative Cooling

Convert Cooling machine (DX machine) to heat pumps Compressor Cooling Sorption cooling Evaporative cooling DX machine Chiller Evaporative Chiller Air Cooled Condenser Water Cooled Condenser Convert Cooling machine (DX machine) to heat pumps

Daily distribution of cooling load

Thermal Storage Make ice/chilled water at times of low demand or low energy prices Store water in insulated container Can be used to reduce overall demand Water can be used as secondary water source for fire protection Ice/snow

Thermal Storage

Thermal storage

Ventilation Air-flow in Buildings http://www.epa.gov/iaq/largebldgs/i-beam_html/qref_01_03.htm

Zones In building How to define the zone in building Based on cooling/heating load requirement Based on ventilation requirement Based on use of buildings – different apartments deferent zones

Air Handling Units (AHU) Control of air Systems Provide conditioned air Heating, cooling, humidification, dehumidification Ventilation Provide fresh air, remove contaminated air

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

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

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

How does a residential thermostat work? Calculates difference between actual temperature and required temperature and adjusts furnace/AC output accordingly Measures temperature continuously and turns equipment on and off when temperature is different from set point temperature Measures temperature continuously and turns equipment on and off when temperature is outside of specified bounds 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°F Require less cooling

Variable Air Volume Single zone VAV Multizone VAV Can also use reheat 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

Reading Assignment Tao and Janis Chapter 3 Chapter 6 (from 6.1 to 6.7) Sections: 3.4.1- 3.4.16 (including 3.4.16) 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 2 Zone 3 Whole building Sensible cooling load for zone Time when the max cooling load appear 41000 Btu/h at 4 PM 45000 Btu/h at 6 PM 27000 Btu/h at 8 AM 92000 Btu/h Sensible cooling load for critical hour for whole building (6 PM) 37000 Btu/h 9000 Btu/h Latent cooling load (internal sources + infiltration) 5400 Btu/h 5200 Btu/h 16000 Btu/h Required amount of fresh air based on number of occupants 240 CFM (12 occupants) 520 CFM (26 occupants) 1000 CFM (50 occupants)

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