Chapter 9: HVAC FOR SMALLER BUILDINGS
This is the first of two chapters that cover HVAC (heating, ventilating, and air conditioning) systems. The focus of this chapter is smaller buildings (residential and small commercial), with a topic organization that proceeds from the need for such systems, to the systems design process, to component locations and sizes, to descriptions of systems and equipment. Although the book has a clear “bias” toward passive solutions, some climates and building types will require the use of mechanical/electrical systems for climate control. An extensive review of such systems is provided.
A process used to design HVAC systems (including complimentary passive systems) is outlined. The various analysis, selection, and sizing activities are organized by design phase. Schematic design addresses general needs and resources, building envelope potentials, passive system opportunities, and preliminary sizing of active systems. During design development, more specific system design requirements are developed, heating and cooling loads are determined, a system or systems are selected, equipment locations are established, equipment is sized, and the system is laid out. During design finalization (development of construction documents), final systems coordination (mechanical with electrical, structural, plumbing, etc.) occurs and the HVAC system decisions and calculations are verified.
The choice between a local or a central system is one of the earliest design decisions. Advantages and disadvantages of both options are reviewed. Preliminary system sizing is discussed. The concept of a “distribution tree is introduced. Controls as a component of HVAC systems are introduced—including thermostats, building management systems, automation systems, and future trends in controls.
The compression and absorption refrigeration cycles are presented as a means of mechanically developing cooling and heating (via a heat pump). Components of compression refrigeration systems are discussed, including conventional and alternative refrigerants and various types of compressors. The issue of CFCs and their connection to global warming is considered. Components and operation of the absorption refrigeration cycle are presented. The relationship of psychrometrics to cooling process and equipment is addressed.
A number of cooling-only systems are presented along with their typical equipment and applications. Such systems include fans, unit air conditioners, misting and roof spray evaporative cooling systems, and evaporative coolers (direct and indirect). Heating-only systems are similarly covered. Such systems include wood heating devices (fireplaces, stoves, pellet stoves, and masonry heaters), electric resistance heating, gas-fired heaters, ceiling mounted electric heating systems, hot water boilers, baseboard and radiator systems, hydronic radiant panels, and warm air heating systems. System zoning and the wide range of equipment and system efficiency ratings are discussed. Systems that will provide both heating and cooling are considered, with an emphasis on heat pumps (air-to-air, water source, and ground source).
9.1 Review of the Need for Mechanical Equipment
9.2 Heating, Ventilating, and Air Conditioning (HVAC): Typical Design Processes
9.3 Equipment Location and Service Distribution
(a) Central or local?
(b) Central heating or cooling equipment
(c) Distribution trees
9.4 Controls for Smaller Building Systems
9.5 Refrigeration Cycles
(a) Compressive refrigeration
(b) Alternative refrigerants
(c) Absorption refrigeration cycle
9.6 Cooling-Only Systems
(a) Fans
(b) Unit air conditioners
(c) Evaporative cooling: misting
(d) Evaporative cooling: roof spray
(e) Evaporative coolers
(f) Indirect evaporative cooling
9.7 Heating-Only Systems
(a) Wood heating devices
(b) Electric resistance heaters
(c) Gas-fired heaters
(d) Ceiling electric resistance heat
(e) Hot water boilers
(f) Hot water baseboard and radiator systems
(g) Radiant panels
(h) Hydronic heating sizing
(i) Hydronic zoning
(j) Heating equipment efficiency, combustion, and fuel storage
(k) Warm air heating systems
9.8 Heating/Cooling Systems
(a) Cooling coils added to warm air furnaces
(b) Hydronic and coils
(c) Air-air heat pumps
(d) Ground source heat pumps
(e) Water source heat pumps
9.9 Psychrometrics and Refrigeration
References
Important Terminology
Important Metrics
The New Buildings Institute (“Small Commercial HVAC System Design Guide”)
http://www.newbuildings.org/mechanical.htm
The Trane Company:
http://www.trane.com/
Carrier:
http://www.carrier.com/HomePage/
York International Corporation:
http://www.york.com/
McQuay International:
http://www.mcquay.com/
U.S. Environmental Protection Agency, Energy Star-Labeled Heating and Cooling Equipment:
http://www.epa.gov/appdstar/hvac/
This chapter addresses HVAC systems for large buildings and is complementary to Chapter 9 (which focuses on small-building HVAC systems). Considerations (such as IAQ) dealt with in previous chapters are referenced as an introduction.
Relationships between HVAC system selection and general building organization are considered in some detail. These basic coordination issues include: HVAC system zoning, matching thermal zones to system capabilities, whether a local or central system is appropriate, design intent relative to uniformity or diversity of the thermal environments within a building, space needs and availability for distribution trees, appropriate location(s) for central equipment components, whether the HVAC system should be concealed or exposed, and whether the HVAC system should be integrated with or kept separate from the building structural system. Options for distribution tree placement are illustrated and reviewed.
Four main classifications of HVAC systems are identified: direct refrigerant systems, all-air systems, air and water systems, and all-water systems. Each of these classifications holds many specific types and arrangements of systems. Direct refrigerant systems generally eliminate the need for a distribution tree but are typically used in smaller buildings; they were discussed in Chapter 9. All-air systems employ only air to provide heat transfer between the central station location and the conditioned spaces. Types of all-air systems include: single zone, multizone, single-duct variable air volume (VAV), fan-powered VAV, single duct with reheat, and double-duct systems. All-air systems require large distribution trees, but are a good choice from a comfort and indoor air quality perspective.
Air and water systems circulate both of these media from central station to conditioned spaces. Most of the heating/cooling is done via the water distribution tree. The air supply is generally provided to assist in maintaining indoor air quality. Air and water system types include (among other options): induction, fan coil with supplementary air, and radiant panel with supplementary air. Water loop heat pumps are included under this classification, but it is noted that they are often considered an all-water system. All-water HVAC systems require only a small distribution tree between central plant and conditioned spaces. Resolution of air quality issues with such systems is described as ambiguous.
Options for equipment placement and space requirements for heating/cooling and air-handling equipment are discussed. Guidelines are given for preliminary sizing of equipment rooms. The individual equipment items that comprise the central equipment for an HVAC system are discussed in turn. Such equipment includes: boilers of various types, chillers (compressive and absorption), condensing water equipment (cooling towers), energy conservation and energy storage equipment, air-handling equipment (including various fan types), and controls. Typical equipment is illustrated, several sample equipment layouts are given, and space requirements summarized.
Elements of air distribution systems are reviewed. Elements addressed specifically include: ducts, ceiling air supply, air supply for underfloor air distribution, and workstation delivery systems. Duct sizing estimates are discussed. Alternatives to conventional air supply/return are presented (for example, the air-extract window, air curtain window, and climate window).
Each of the named system types (VAV, induction, etc.) introduced at the beginning of the chapter is considered in greater detail. System characteristics are reviewed and typical applications discussed. Example buildings are employed to illustrate actual installations for some of the systems. Delivery and auxiliary equipment specific to certain systems is described and illustrated.
District heating and cooling is introduced. Cogeneration is defined; cogeneration history and applications are presented. Fuel cell applications for buildings are considered.
10.1 HVAC and Building Organization
(a) Zoning
(b) System anatomy
(c) Central versus local systems
(d) Uniformity versus diversity
(e) Comparing systems and zones
(f) Distribution trees
(g) Central equipment location
(h) Concealment and exposure
(i) Mechanical-structural integration or separation
(j) Distribution tree placement options
10.2 HVAC System Types
(a) Direct refrigerant systems
(b) All-air systems
(c) Air and water systems
(d) All-water systems
(e) Equipment space allocations
10.3 Central Equipment
(a) Boilers
(b) Chillers
(c) Condensing water equipment
(d) Energy conservation equipment
(e) GeoExchange systems
(f) Energy storage
(g) Air handling equipment
(h) Controls
10.4 Air Distribution within Spaces
(a) Air ducts
(b) Ceiling air supply
(c) Underfloor supply with displacement ventilation
(d) Workstation delivery systems
(e) Alternative supply/return systems
10.5 All-Air HVAC Systems
(a) Single-zone systems
(b) Single-duct VAV systems
(c) Fan-powered VAV systems
(d) Multizone systems
(e) Single duct with reheat
(f) Double-duct systems
10.6 Air and Water Systems
(a) Induction
(b) Fan-coil with supplementary air
(c) Radiant panels with supplementary air
(d) Water loop heat pump
10.7 All-Water Systems
10.8 District Heating and Cooling
(a) High-temperature water and chilled water
10.9 Cogeneration
(a) Electrical power generation at the site
(b) Early on-site power generation
(c) How cogeneration developed
(d) Turbines and reciprocating engines
(e) Cogeneration for housing
(f) Fuel cells
References
all-air (a system category)
air and water (a system category)
all-water (a system category)
Important Terminology
single-zone system
VAV (variable air volume) system
fan-powered VAV system
multizone system (a specific system type--not the same as multiple zone)
reheat
double-duct system
two-pipe system
four-pipe system
induction (system or unit)
fan-coil (system or unit)
radiant panel
modular boiler
pulse boiler
breeching
stack
flue
combustion air
chilled water
condensing water
fan (panel; vaneaxial--fixed, variable-pitch, adjustable-pitch; centrifugal)
duct (ductwork)
diffuser
grille
register
Important Metrics
The Trane Company:
http://www.trane.com/
Carrier Corporation:
http://www.global.carrier.com/
York International Corporation:
http://www.york.com/
McQuay International:
http://www.mcquay.com/
U.S. Environmental Protection Agency, Energy Star-Labeled Heating and Cooling Equipment:
http://www.energystar.gov/index.cfm?c=heat_cool.pr_hvac
Source: http://www.areforum.org/up/Mechanical%20and%20Electrical/MEEB/ch09.doc
http://www.areforum.org/up/Mechanical%20and%20Electrical/MEEB/ch10.doc
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