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HVAC System Selection Guide

Determining a building's heating and cooling loads is the second step in selecting an HVAC system. The loads establish the system's capacity needs. Cooling loads and humidity requirements are used to size air conditioning systems, while heating or ventilation may be more important for other systems. When installing a system in an existing building, the new system must be compatible with existing equipment, ductwork, and piping, and fit in the existing space. System selection should consider financial factors, building conditions, usage, energy availability, and control schemes.

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63 views2 pages

HVAC System Selection Guide

Determining a building's heating and cooling loads is the second step in selecting an HVAC system. The loads establish the system's capacity needs. Cooling loads and humidity requirements are used to size air conditioning systems, while heating or ventilation may be more important for other systems. When installing a system in an existing building, the new system must be compatible with existing equipment, ductwork, and piping, and fit in the existing space. System selection should consider financial factors, building conditions, usage, energy availability, and control schemes.

Uploaded by

Rohit Shrestha
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Choosing an HVAC System 221

Step two in the selection process is determining the


building’s heating and cooling loads. For example, is the cooling
load mostly sensible or latent? Is the load relatively high or low
per square foot of conditioned area as compared to other similar
buildings? Is the load uniformly distributed throughout the con-
ditioned space? Is it relatively constant or does it vary greatly?
How does the load vary with time and operating conditions?
Determining the heating and cooling loads establishes the
system’s capacity requirements. Cooling loads and humidity re-
quirements are used to size air conditioning (comfort and process
cooling) systems. In other systems, heating or ventilation may be
the critical factors in sizing and selection. For example, a building
may require a large air handling unit and duct system to provide
huge quantities of outside air for ventilation or as make-up air to
replace air exhausted from the building. In other buildings, in
colder climates for instance, heating may be the determining fac-
tor on equipment size. The physical size of the equipment can be
estimated from the heating and cooling load information alone.
This information can help to reduce the choice of systems to those
that will fit the space available.
There are also choices to be made depending on whether the
system is to be installed in a new building or an existing building.
In existing buildings, for example, the HVAC system was de-
signed for the loads when the building was built. This means if
new systems are to be integrated with existing ones (in order to
keep costs down or for other reasons), the new or retrofitted sys-
tems must be adaptable to existing equipment, ductwork and
piping, and new equipment or systems must fit into existing
spaces. If new systems are to perform properly when tied in with
existing systems, the old and the new must be looked at carefully
and in its entirety. The designer will need to determine how a
change to one part of a system will affect another part and a how
a change in one system will affect another system. The number of
choices is narrowed further to those systems that will work well
on projects of a given application and size and are compatible
with the building architecture.
222 HVAC Fundamentals

SYSTEM SELECTION GUIDELINES

Each of the following issues should be taken into consider-


ation each time an HVAC system is selected.

• Financial factors
Initial cost
Operating costs
Maintenance and repair cost
Equipment replacement or upgrading cost
Equipment failure cost
Return on investment (ROI)
Energy costs

• Building conditions
New or existing building or space
Location
Orientation
Architecture
Climate and shading
Configuration
Construction
Codes and standards

• Usage
Occupancy
Process equipment

• Energy availability
Types
Reliability

• Control scheme
Zone control
Individual control

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