ASHRAE Journal - July 2024 - 40

TECHNICAL FEATURE
FIGURE 7 Energy consumption plot for TDHP and MSHP systems
(06/04/2021-10/13/2021).
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Energy
TDHP
MSHP
Linear TDHP
Linear MSHP
and airflows. The focus of this study was to determine
the differences in temperature and humidity control
over an entire duration of a cooling season in a hot and
humid climate over a broad range of conditions that
persist over the course of several months.
Conclusions
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Total Enthalpy Load (kJ/kg)
using the energy data curve fit in Figure 7, we predicted
cooling energy consumption for both TDHP and MSHP
systems when each operated individually throughout
the entire cooling period. The results also indicated
that the MSHP system consumes approximately 29%
more energy than the TDHP system given the same
seasonal weather conditions. The energy consumption
trend is self-explanatory because as the load increases,
the energy consumption also increases.
Study Limitations and Potential Sources of Error
The research was conducted at a single location over
an entire cooling season in an unoccupied research
house. Climate conditions, building structures and
occupant behaviors can vary significantly across
different regions, affecting HVAC system performance
differently. This study was performed focusing on a
single make and model for each system type, which
limits the potential variations across different models
and brands. Although efforts were made to replicate
the ducted system's zoning configuration in the
multisplit system, there could still be differences in
how the systems distribute air and control humidity
due to variations in duct design, air distribution and
system controls.
It is also worth noting that there is no direct
comparison between the sensible/latent heat ratios of
the heat exchangers during the cooling season of this
study. To make such comparisons, it would require
heavily instrumented systems in tightly controlled
laboratory conditions. Even then, the conclusions
would be limited because the sensible/latent heat
ratios of a system vary significantly and nonlinearly
with changing indoor temperature and humidity
conditions as well as for different compressor speeds
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This study presented a performance and cost
comparison between a zoned traditional ducted
variable speed heat pump (TDHP) and a multisplit
heat pump (MSHP) system operating on the same
home over the same cooling season. The research
was conducted at the research facility located in the
University of Texas at Tyler situated in U.S. Climate
Zone 3. Indoor temperature, indoor relative humidity,
energy consumption and weather data were acquired
for the summer of 2021 from June to October and used
to perform the comparison based on temperature,
humidity control and energy consumption. The results
showed that the TDHP was able to provide better
temperature control in the house by keeping the
temperature closer to the setpoint and maintaining
better spatial temperature uniformity compared
to the MSHP system. The TDHP also demonstrated
significantly better dehumidification capabilities
by maintaining the average relative humidity in the
house at 45% with a maximum value of 50%, while
the average relative humidity in the house during the
operation of the MSHP system was 58% with humidity
values reaching as high as 64%. The results also showed
that the MSHP consumes 29% more energy compared
to the TDHP if operated for the entire cooling season,
despite the two systems having similar hang-tag
efficiency ratings.
References
1. Ashley, T.D., C.E. Metzger, J.T. Kolln, G.P. Sullivan. 2020.
" Maximizing the Use of Ductless Mini-Splits in Homes with
Existing Central or Zonal Heating and Cooling Equipment. " Pacific
Northwest National Laboratory.
2. Martin, E., C. Withers, J. McIlvaine, D. Chasar, D. 2018.
" Evaluating Moisture Control of Variable Capacity Heat Pumps in
Mechanically Ventilated, Low-Load Homes in Climate Zone 2A. "
DOE/EE-1702. Florida Solar Energy Center.
3. Withers, C. 2018. " Optimizing Energy Efficiency and
Improved Dehumidification Performance of Variable Capacity Air
Conditioning Systems. " ACEEE Summer Study on Energy Efficiency in
Buildings.
4. ACCA. 1997. " Manual RS-Comfort, Air Quality, and Efficiency by
Design. " Air Conditioning Contractors of America, Inc.
Energy Consumption (kWh)
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ASHRAE Journal - July 2024

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