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Chapter 3. HVAC Delivery Systems

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1 Chapter 3. HVAC Delivery Systems
3.2 What principles are used to vary the amount of HVAC service to a space with varying loads? 1) Constant-Temperature, Variable Volume(On-Off) 2) Single-Zone Constant Air Volume 3) Single-Zone Reheat 4) Constant-Volume Terminal-Reheat, Multiple Zones 5) Constant-Volume Dual Duct 6) Multizone(CAV) 7) Single-Zone Variable Air Volume(VAV) 8) Multiple-Zone Variable Air Volume 9) Variable Air Volume Reheat Terminals 10) Variable Air Volume Dual Duct 11) Variable Air Volume Multizone 12) Fan Terminal Units 13) Fan Coils 14) Radiant Panel Heating and Cooling 15) Package Terminal Air Conditioners 16) Water-Source Heat Pumps

2 3.4. Which HVAC delivery systems are best for preventing high humidity in spaces? Why?
3.6 Name the HVAC delivery systems that are most flexible for adding or rearranging zones. Why are they effective in this respect? 3.8 Which HVAC delivery systems would be most appropriate in a building in which risk of water damage is a serious concern? 3.10 Of all the HVAC delivery systems discussed in this chapter, which is the most energy-efficient? Why? 3.12 When is it appropriate to use two-position control?

3 3.14 A hotel developer is deciding whether to use fan coils or PTAC units. How would you counsel him or her on matters of cost and quality? 3.16 You are helping an owner decide between VAV terminals and FTU terminals for interior conference rooms in a new office building. How would you counsel the owner on matters of cost and quality? 3.18 How are water-source heat pumps and PTAC unis similar? How are they different?

4 Signal 1) Two-position signal
input signal : indicate the operating status of the equipment (on or off, normal or alarm, open or close) output signal : start, stop, open, or close the controlled equipment 2) Proportional signal monitor and control temperature or pressure, or flow provide multiple levels of control and alarm

5 Fig. 3-6 Single-zone constant-volume reheat system
3.4.3 Single-Zone Reheat Constant volume system  applied for humidity control Hospital operating room, computer rooms System control: Humidistat is used for adjusting air temperature Fig Single-zone constant-volume reheat system

6 3.4.5 Constant – Volume Dual Duct
Systems send warm and chilled air through a pair of main trunk ducts to the areas being served Are capable of controlling multiple zones, with each zone served by an individual mixing box Cooling : damper operate to deliver more chilled air and less warm air Heating is converse Total airflow stays fairly constant Warm air Chilled air Mixing box Constant airflow

7 3.4.10 Variable Air Volume Dual-Duct Terminal
Two air valves in a common VAV box Hot air damper and a cold air damper Minimal overuse of energy due to mixing air Energy efficient (rather than VAV with convector and VAV reheat) Electric or hot-water devices are not required at the perimeter Fig Variable air volume dual-duct system

8 3.4.12 Fan Terminal Units Fan terminal Units
VAV decrease the flow of cooling air under light load condition Fan terminal contains a VAV damper that respond to the space thermostat Chilled air through VAV damper is mixed with return air and delivered to the space via a small constant-volume fan

9 Fig. 3-24 Fan terminal units
The fan have a short length for distribution, their pressure requirements are low, and energy consumption is accordingly modest Overall energy savings are achieved at the central fan Fan terminal can also be equipped with heating coils and are sometimes used in combination with VAV systems Fig Fan terminal units

10 Fan Terminal Units Split system : single-duct VAV(interior) & hot-water convector(exterior) All-air system : single-duct VAV(interior) & dual-duct VAV(exterior) all air system is usually lower in cost, but more space

11 3.4.14 Radiant Panel Heating and Cooling
hot and chilled water circulates through tubing convection and absorbing heat between space and panel Combination ventilation air system(latent cooling and supplementary sensible cooling) Energy-efficient reducing fan power for the portion of the load Fig. 3-28 (a) Section through radiant panel shows water tube bonded to ceiling plate. (b) Radiant panels used to heat and cool at perimeter, cool only at interior

12 3.4.15 Package Terminal Air Conditioners
PTACs contains compressors and air-cooled condensers noisy and require high maintenance as their compressors age PTACs can reverse the refrigeration as a heater

13 3.4.16 Water-Source Heat Pumps
Unitary(contain compressors) terminal devices reversible refrigerant cycle for heating and cooling Cooling mode the coil absorb heat from the air to boil refrigerant suction gas is compressed in the compressor and hot gas is condensed in the refrigerant-to-water heat exchange Heating mode the refrigerant flow circuit is reversed by a reversing valve the coil acts as a condenser and the heat exchanger acts as an evaporator

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