Michael BrandemuehlUniversity of Colorado 1HVAC Systems: OverviewMichael J. Brandemuehl, Ph.D, P.E.University of ColoradoBoulder, CO, USAOverview System Description Secondary HVAC Systems Air distribution Room diffusers and air terminals Duct Design Fan characteristics Air Handling Units Water distribution Cooling coils Pipes and pumpsPrimary HVAC Systems Electric chillers Air and water cooled Compressor technologies Performance Thermal chillers Absorption Engine-driven Cooling towers Overall Design ProcessMichael BrandemuehlUniversity of Colorado 2System Overview Core Objectives: healthy, productive, comfortable indoor environment Heating to perimeter spaces Cooling to perimeter and core spaces Humidification or dehumidification as needed Ventilation to occupied spaces Deliver over time and spaceTime and Space HVAC needs in each room change over day and over year At any time, may need heating and cooling in different rooms of building Core needs cooling even in winter HVAC system must meet simultaneous diverse loadsMichael BrandemuehlUniversity of Colorado 3System Options Separate HVAC system for every zone Residential Motel Strip mall One HVAC system for entire building Distribute heating, cooling, ventilation to individual zonesTypical Home System(AIR CONDITIONING)AIRFLOWAIRFLOW(WITH FAN AND FILTER)Michael BrandemuehlUniversity of Colorado 4Typical Large Commercial SystemDistributed HVAC Systems Packaged terminal air conditioner (PTAC) Water loop heat pump (WLHP) Packaged rooftop unit (RTU)Michael BrandemuehlUniversity of Colorado 5Typical Small Commercial System With Rooftop UnitsPackaged Rooftop Unit (RTU)Michael BrandemuehlUniversity of Colorado 6Slab Installation with Side DischargeTypical Small Commercial System With “Split System”Michael BrandemuehlUniversity of Colorado 7Water Loop Heat Pump SystemSystem Characteristics Rooftop Units (RTU) or Split Systems One unit each “zone” Refrigerant in cooling coil Ventilation Ceiling diffusers and ductwork Simple controls – one thermostat per zone Separate billing for each tenant Sometimes separate boiler and radiatorsMichael BrandemuehlUniversity of Colorado 8Zoning One thermostat per zone Rooms with similar load profiles Good: offices on same side of building Bad: exterior office and interior conf. rm. Proximity (one thermostat!) Air communication allows larger zones Recognize local loads in large spacesCentral HVAC System Terminal devices Fan coil units Air and water distribution systems Heat exchangers Central heating and cooling sourcesMichael BrandemuehlUniversity of Colorado 9Typical Central SystemPackaged Central SystemMichael BrandemuehlUniversity of Colorado 10Large Central System EquipmentTypical Large Central SystemMichael BrandemuehlUniversity of Colorado 11Benefits of Central and Distributed System Designs Large equipment has higher quality, efficiency, and durability Maintenance is concentrated Noise is removed from zone Diversity allows lower installed capacity Can use thermal storage Easy to provide zoning Direct control by occupants Easier independent scheduling for energy savings Generally lower capital costs and shorter lead time for equipment Don’t need dedicated maintenance staff, use service contract Can often install on roof, less useable space for equipmentCentral DistributedTypical Design Approach Start at the zone and work out Loads Air diffusers and zone terminals Air distribution system Air handlers Chilled water distribution Central cooling and heat rejectionMichael BrandemuehlUniversity of Colorado 12Meeting Zone Loads)()(SARApSAsenSARASAtotTTcmQhhmQ−=−=Given controlled room air temperature, can control airflow or supply temperature to meet changing sensible loadsSupply Air (SA)Return Air (RA)Loads Qtotand QsenControlled RoomConditionsAir Handling Systems (All Air) Constant air volume (CAV) systems Constant zone airflow Meet varying loads with varying supply air temperature Variable air volume (VAV) systems Constant zone supply air temperature Meet varying loads with varying supply airflowMichael BrandemuehlUniversity of Colorado 13Air Handling Systems (cont.) Dual duct (DD) systems Mix hot and cold air at each zone Use constant or variable supply airflow Multizone (MZ) system Mix hot and cold air for each zone at the air handlerTypical CAV AHU SystemMichael BrandemuehlUniversity of Colorado 14Typical VAV AHU SystemTypical Dual Duct SystemMichael BrandemuehlUniversity of Colorado 15Typical Multizone SystemAir-Water Systems Use combination of conditioned air and zone water coils Ventilation requires air Zone heating and cooling loads can be met with fan coilsMichael BrandemuehlUniversity of Colorado 16Fan Coil One or two coils (use seasonal valves if one coil for both hot and cold water) Thermostat controls water flow Ventilation must be met with conditioned or unconditioned outdoor airFan Coil System: 4 PipeMichael BrandemuehlUniversity of Colorado 17Fan Coil System: 2 PipeIntegrated With Central SystemMichael BrandemuehlUniversity of Colorado 18General System Classification Secondary HVAC Equipment and Systems Generally in the building Air distribution Water distribution Air handlers and fan coils Primary HVAC Equipment and Systems Primary sources of heating and cooling Chillers and heat rejection Boilers Engines and generators Thermal StorageAir Delivery to Zone Fully mixed zone Supply air is mixed uniformly with room air Air can be introduced at ceiling, walls, floor Displacement ventilation Supply air is slowly introduced at floor Air rises, absorbing heat and pollutantsMichael BrandemuehlUniversity of Colorado 19Mixed vs. DisplacementTypical DiffusersMichael BrandemuehlUniversity of Colorado 20Diffuser Selection Mix air without causing draft, quietly, with low pressure drop Velocities less than 50 fpm (0.25 m/s) in occupied zone Diffuser manufacturers report throw: distance till velocity is reduced to specified level Beware of change in throw at reduced airflowAir Terminals Control supply airflow entering zone (VAV) Control supply air temperature (CAV & VAV) Interact with zone thermostatMichael BrandemuehlUniversity of