Building America Case Study
Technology Solutions for New and Existing Homes
FSEC Side-by-Side Laboratory TO-5
Report – Effect of Ducted HPWH on
Space Conditioning and Water
Heating Energy Use
Cocoa, Florida
_________________________
PROJECT INFORMATION
Project Name: Flexible Residential
Test Facility - Effect of ducted HPWH
on space conditioning
Location: Cocoa, Florida
Partners:
Building America Partnership for
Improved Residential Construction,
www.ba-pirc.org
Building Components: HVAC and
Water Heating
Application: Single Family
Year Tested: 2014-2015
Applicable Climate Zone(s): Hot-Humid
_________________________
PERFORMANCE DATA
Potential cooling energy reduction (180
days): 1.95 kWh/day.
The Building America Partnership for Improved
Residential Construction (BA-PIRC) investigated
the effect of ducted heat pump water heaters
(HPWH) on space conditioning energy use and
water heating. To assess HPWH ducted ventilation
strategies and impact on air conditioning under a
hot-humid climate, the Florida Solar Energy Center
conducted controlled experiments in two
geometrically-identical, full-scale, side-by-side
residential research facilities known as the flexible residential test facility
(FRTF). While both buildings are built with concrete slab on-grade, the only
difference between these two was the floor material used – carpet and bare
concrete floors. On average these two homes measured 20 kWh/day of
energy consumption on their primary HVAC equipment (SEER 14) during
the cooling season without HPWH ventilation. Savings of 2.0 kWh/day or
10% reduction, were achieved by using the interior (balanced) HPWH
airflow path configuration during cooling season. However, when using an
outdoor to interior (pressurized building) airflow path configuration a 2%
(+0.375 kWh/day) penalty on the primary HVAC system is incurred.
Heating season in central Florida is not as severe as in other parts of the
country. The buildings utilized 4.8 kWh/day on average baseline during the
heating season. With ventilation, heating increases as shown in figure below.
Heating season increase (80 days):
Interior configuration = +2.0 kWh/day
Outdoor air = +3.6 kWh/day
Duct Kit: $319 (inlet/Outlet)
Duct Install Cost: $619
Data for experiments conducted in the
FRTF is available through
www.infomoinitors.com/rtf/
Feb
Jan
Dec
Nov
Oct
Sep
Aug
Jul
-5
5
kBtu's /day
Outside Air to Interior
15
Interior to Interior
25
Building America Efficient Solutions for New and Existing Homes Case Study: Effect of Ducted HPWH on Space
Conditioning and Water Heating Energy Use
Ducted Heat Pump water Heater
Lessons Learned
 Ventilation (cooling) provided through the exhaust of a HPWH is a function of
runtime, which is influenced primarily by the seasonal hot water gallons used and
thermostat setting.
 When using interior to interior HPWH ducted airflow configuration, data indicates
that primary HVAC equipment energy consumption for the cooling season is
reduced by 9.7% (1.94 kWh/day) on average for the 3 bedroom (1535 sq. ft)
buildings. That is, 9.5% (1.91 kWh/day) electric energy reduction for the carpeted
floor building and 10.0% (1.97 kWh/day) reduction for the bare concrete slab
home.
 When using outside air to interior ducted airflow path configuration (presurized
building), primary HVAC equipment energy consumption for cooling season
increases by 1.9% (+0.375 kWh/day) on average. That is, 0.6% (0.12 kWh/day)
electric energy reduction for the carpeted floor building and 3.2% (0.63 kWh/day)
reduction for the bare concrete slab building.
Heat pump water heaters were
retrofitted with duct kits (shown without
insulation) and manual directional
dampers to study controlled ventilation
strategies.
Gallons / day
0
10
20
30
40
50
60
Feb
 A ducted HPWH in balanced interior airflow configuration increased heating
energy consumption of the building by 20.5% (1.0 kWh/day) on average compared
to the baseline of 4.85 kWh/day over the heating season (Dec 2014 thru Feb 2015)
 A ducted HPWH using outside air into the interior air flow pathway (pressurizing
building) increased heating energy consumption of the building by 75.6% on
average. The additional heating energy recorded had a much larger difference
beween the two distinct floors of the buildings. The carpeted building heating
energy consumption increased by 110.3% (5.274 kWh/day) on average while the
building wioth bare concrete floor increased 41.2% (2.7 kWh/day) when compared
to the average heating baseline of 4.85 kWh/day
 Cooling efficiency demosntrated by the HPWH was measured and averaged across
all ventilation configurations resulting in a COP of 1.5 (1.12 to 1.9).
Jan
 Sensible heat ratio (SHR) of the unit cooling capability was lowered due to the
reduction of airflow by the ducted configurations -- Manufacturer claims 450 cfm
for non-ducted vs. 148-160 cfm as measured for ducted HPWH. SHR’s calculated
as 0.62 0.70 and 0.54 for the kit restricted baseline case, interior to interior and
outside to interior ducted configurations.
Dec
Nov
Oct
 Seasonal hot water heating efficiency of the HPWH’s was determined showing
little variation for the seasonal hot water load imposed (34 to 53 gpd) averaging a
COP of 2.0 and 2.1 for the east and west FRTF buildings.
Sep
Aug
Jul
0
50 100 150 200 250 300
HPWH runtime (min.)
runtime
gals/day
 Using the outdoor air to interior HPWH airflow configuration may help meet
ASHRAE 62-2 ventilation depending on infiltration rate of building: 48% to 28%
for buildings with ACH 8.0 to 3.0 espectively
Looking Ahead
With proper duct design and mechanical controls, HPWH’s can contribute to
reduce building cooling. Further studies are encouraged for colder climates to add
a hydronic HPWH loop (e.g., garage install) to preheat outside air seasonally.
www.buildingamerica.gov
LAB-XX-XXXX March 2015
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