ASHRAE Journal - February 2023 - 18

COLUMN ENGINEER'S NOTEBOOK
TABLE 3 System options and comparison.
GAS FIRED BOILERS
OPTIONS
HEATING
CAPACITY
(MBH)
Base
Case
Option
1: HP
Chiller
Option
2: HR
Chiller
Option 3:
Hybrid
Plant
6,200
N/A
N/A
4,000
MINIMUM
HEATING
CAPACITY
(MBH)
310
N/A
N/A
200
PEAK
HEATING
EFFICIENCY
(COP)
0.9
N/A
N/A
0.9
HEATING
CAPACITY
(MBH)
N/A
8,300
6,400
2,200
MINIMUM
HEATING
LOAD (MBH)
N/A
690
530
220
the HRC is operating at low-load conditions (and higher
ambient temperatures) and 135°F (57°C) when the gasfired
boilers are operating at peak heating needs. In this
case, the HRC equipment COP is approximately 7.0. The
HRC requires pumps on the chilled water side to ensure
the chiller modules maintain the required differential
pressure drop across the heat exchanger. Gas-fired boilers
are designed as part of the system for condensing temperatures
and will operate during peak loads, when the
HRC can no longer maintain system loads.
Table 3 provides an overview of assumptions for each
option compared to the baseline natural gas-boilers.
This methodology is used to simplify the calculations
FIGURE 2 Operational carbon analysis.
700%
600%
500%
400%
300%
200%
100%
0%
Base Case:
Gas-Fired Boilers
Option 1:
All-Electric HP
Emission Factors:
Electrical grid CO2 Emissions: 453.2 lb/MWh,3
Natural gas CO2 Emissions: 53.11 kg/MBtu.4
18
ASHRAE JOURNAL ashrae.o rg
F E B R U A RY 2023
Option 2: All-Electric
HR Chiller
Option 3:
Hybrid Plant
138
608
326
236
608
HEAT PUMP TECHNOLOGY
CHW
EFFICIENCY
(COP)
N/A
2.2
N/A
N/A
CAPACITY
(TONS)
N/A
730
365
145
FULL LOAD
HEATING
COOLING
EFFICIENCY
(COP)
N/A
9.728
N/A
N/A
SYSTEM
EFFICIENCY
(COP)
N/A
N/A
5.3
8.5
EQUIPMENT
WEIGHT
ELECTRICAL
- MOP
@480V/
3PH
6,000
50,000
18,500
9,500
*
CENTRAL
EQUIPMENT
COST ($)
$200,000
1,600 $1,600,000
800
250
$600,000
$400,000
and evaluate the options at a high level. Figure 2 compares
the annual carbon impacts. For simplicity, a more
detailed life-cycle cost analysis (LCCA) has not been
included here but should be considered for any project.
Table 3 provides a quick overview and comparison of
system options. Option 1 is a fully independent heating
system but presents significant challenges related to
weight, physical size, electrical requirements and first
costs. The existing facility that would house the new
heat pump equipment (Building B) has an 800A electrical
service, which would require Option 1 to upsize the
electrical service to the building. Option 2 presents a
similar challenge. These electrical upgrade costs have
not been factored into Table 3 and would further impact
the return on investment (ROI) on such a project.
Option 3 is the only viable option of those presented
here, without requiring an upgrade to the electrical
infrastructure. To confirm Option 3 was viable, a meter
read of the facility was performed, which determined
the actual load (plus a 25% safety factor) was 343A of the
total available 800A.
One of the project's main KPIs was to understand the
carbon impacts of the proposed system. Option 1 is an
improvement from the base case; however, the COP
of 2.12 for an air-source heat pump does not give the
desired impact compared to a gas-fired boiler with a
peak efficiency of 96% at a fraction of the cost for the
equipment. Option 2 is the most desirable from an operational
carbon perspective, but is still limited based on
first costs and impacts to the existing building's electrical
infrastructure. Option 3, the hybrid plant, provides a
C02 Emissions
http://ashrae.org
ASHRAE Journal - February 2023

Table of Contents for the Digital Edition of ASHRAE Journal - February 2023
