ASHRAE Journal - July 2024 - 35

TECHNICAL FEATURE
of Texas at Tyler. This research
house is located in U.S. Climate
Zone 3, characterized as hot and
humid. The research house is a
conventionally designed home with
energy-effi cient features that grant
a home energy rating system (HERS)
index of 65, where standard new
and existing homes index at 100 and
over. The dwelling encompasses a
conditioned space of approximately
150 m2 (1,600 ft2) and includes three
bedrooms and two bathrooms.
The design features an open-concept
FIGURE 1 Systems' layout, TDHP on left and MSHP on the right.
TDHP
MSHP
Supply
Return
Master
Bedroom
Dining
AHU
Living
Kitchen
Front
Bedroom
layout, encompassing the kitchen,
dining area and living room. This
study divided the research facility into
two zones: Zone 1 comprised three
bedrooms and a common bathroom,
while Zone 2 represented the open space. The house
featured both a TDHP and a MSHP system, delivering
conditioned air to all zones. The home had minimal
furnishings and was unoccupied, so outdoor heat gain
was the primary source of thermal load.
HVAC Systems
The process of selecting and installing HVAC systems
at the research facility commenced with the acquisition
of initial cost estimates from various contractors. Several
were approached, and their bids were obtained to gain
insights into the system recommendations provided by
different installers and the associated up-front costs.
TABLE 1 Contractors' cost and description of systems offered.
CONTRACTOR
TOTAL BID
TDHP MSHP
Contractor A $10,019 $9,700
TDHP
2 ton zoned
variable speed
ducted system.
Contractor B $11,830 $20,350
3 ton zoned
variable speed
ducted system.
Contractor C $20,780 $23,217
2 ton zoned
variable speed
ducted system.
EQUIPMENT
MSHP
2.5 ton multisplit
heat pump with one
low-profi le concealed
duct unit and one ceiling
cassette unit.
3 ton multisplit heat
pump system with one
wall mounted air handler
and two ducted air
handlers.
2 ton multisplit heat
pump system with
one wall-mounted air
handler and two ducted
air handlers.
Middle
Bedroom
Kitchen
Front
Bedroom
Dining
Cassette Unit
Living
Middle
Bedroom
Supply
Return
Master
Bedroom
Table 1 presents a summary of the proposed systems and
their installation cost from three different contractors
and includes any demolition or additional installation
requirements. The research team decided to hire
Contractor A to install the systems.
The ducted system featured a 2 ton (7 kW) variable
speed heat pump with 750 compressor speed stages
with zoning and modulating dampers, along with four
supply registers in Zone 2 and one in each bedroom
and bathroom in Zone 1. The multisplit system
included a 2.5 ton (8.8 kW) cold climate heat pump
with a ceiling cassette unit in Zone 2 and a low-profi le
concealed duct unit in Zone 1, replicating the ducted
system. Zone 1 had one supply in each bedroom and
bathroom, while Zone 2 used a four-way supply and a
single return. Online Table 1 shows the parameters of the
systems installed and Figure 1 illustrates the layout of
the system. (Visit https://tinyurl.com/JournalExtras for
Online Table 1, Online Table 2 and Online Figure 1.)
The fundamental technologies of the vapor
compression cycles of the TDHP and MSHP are
the same; however, the key differences are the
methodology with which capacity is delivered
throughout the house. While both systems typically
use a single outdoor unit that comprises a compressor,
heat exchanger, fan and expansion device, a
TDHP uses a single air handler that comprises a
refrigeration coil, a blower and an expansion device
J U LY 2 0 2 4 ashrae.org ASHRAE JOURNAL
35
Concealed Duct Unit
https://tinyurl.com/JournalExtras http://www.ashrae.org
ASHRAE Journal - July 2024

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