Topic 2. ME 414/514 HVAC Systems Overview Topic 2. Equipment. Outline

Transcription

1 ME 414/514 HVAC Systems Overview Equipment Outline 2-1 The Complete System 2-2 The Air-Conditioning and Distribution System 2-3 Mechanical Equipment Air-handling Equipment Heating Equipment Boilers Furnaces Refrigeration Equipment Compressors reciprocating, scroll, rotary, centrifugal Pumps and Piping Controls and Instrumentation 2-4 All-Air Systems Single-air System Reheat System Variable-volume System Dual-duct System Multi-zone System Low Temperature System 2-5 Air-and-Water Systems Air-Water Induction System Fan-Coil Conditioner System 2-6 All-Water Systems 2-7 Unitary Air Conditioners Room Air Conditioners Through-the-wall Conditioner System 2-8 Heat Pump Systems Heat Pump Types Ground-coupled Closed Loop Systems 2-9 Heat Recovery Systems 2-10 Thermal Storage A complete system is illustrated below. 1

2 Schematic for a typical commercial HVAC system HVAC Zones Zone a space requiring separate thermostatic control. Spaces with uniform loads large, open areas with small external loads. For example, auditoriums, stores and theaters. Spaces requiring precision control areas that require strict control of cleanliness, humidity, temperature, or air distribution. For example, clean rooms, computer rooms, hospital operating arenas. Multiple systems for large areas several zones serviced by one or more systems. For example offices, factories. Very large installations many buildings served by a central plant. For example, college campuses, research facilities, industrial parks. Mechanical Equipment Chapter 11 provides an overview of the mechanical equipment used in most HVAC installations. HVAC Systems Load Control (sensible heat) = mc ( T T ) Q = ρvc ( T T ) Q p exit inlet p exit inlet 2

3 All-Air Systems In these systems all heating and cooling (sensible and latent) is done by supplying air to the conditioned space. A few examples are given below. Figure 1. Residential or small office gas furnace and central air conditioning. Similar to Figure 11.8 in textbook. Figure 2. Diagram for an air handling unit (AHU) for sealed commercial building. Also called the mixing chamber or mixing plenum. Similar to Figure in textbook. 3

4 Figure 3. Diagram of packaged roof-top unit with vapor compression cooling and gas heating. Similar to Figure of text. Figure 4. Photograph of packaged roof-top unit with vapor compression cooling and gas heating. Similar to Figure 11.9 of text. 4

5 Figure 5. Dual duct fixed volume HVAC system for a sealed commercial building. Figure 6. Variable air volume HVAC system for a sealed commercial building. 5

6 Air-Water Systems Conditioned air and water and supplied to a terminal unit at a zone. Figure 7. Air-Water System Schematic The terminal units can take on many different configurations. One example is shown here. Figure 8. Induced air terminal unit for air-water system. 6

7 All-Water Systems Air is heated and cooled at a terminal unit within the zone. Water is conditioned by a central plant and pumped to the zone terminal unit. Figure 9. All-water system schematic. Figure 10. Room-based terminal unit for an all-water system. 7

8 Other HVAC systems: Unitary air conditioners (cooling), for example, window air conditioners Evaporative coolers Heat pumps (heating and cooling) Heat recovery systems Variable refrigerant flow systems Other systems are described in the ASHRAE HVAC Systems and Equipment Handbook. All-Air Systems Advantages Disadvantages Mechanical Equipment can be isolated. Additional duct clearance required. This can reduce usable floor space and increase building height. Complete absence of drain pipes, electrical Air balancing is difficult and requires great wiring, and filters at the conditioned space. care. Seasonal changeover very simple and easy to automate. Very flexible heating and cooling can occur in different zones simultaneously. Terminal units have no fans, motors, or compressors. Air-Water Systems (Induction Systems) Advantages Disadvantages Rooms can be individually controlled at Controls tend to be more complex relatively low cost. (compared to an all-air system). Size of the central air-handler can be Secondary air can cause induction coils to reduced. foul. Filtering can be done at the terminal unit, however this requires frequent inroom maintenance. A low chilled-water temperature is needed to accurately control humidity levels. All-Water Systems Advantages Disadvantages Central air-handlers and ductwork are not More maintenance required. Often, the required maintenance is done in occupied areas. Unused zones can be shutdown form Units that have condensate and drip pans central control. must be flushed and cleaned. Individual room control with little or no Filters are small, low in efficiency and chance of cross-contamination of require frequent replacement. recirculated air from one space to another. Easier to retrofit to existing buildings. Ventilation is usually accomplished by opening windows or by installing outside wall vents. Can save on fuel costs. 8