ASHRAE Journal - September 2021 - 9

LETTERS
storage for use). More important,
the scrubbing approach may be
admissible in normal times, which
does not necessarily apply for
COVID-19 and like viral pandemics,
especially in schools.
To reduce the indoor spread of
viral infections, ASHRAE has already
put limits on a minimum 100%
fresh air supply, and this limit may
void the energy savings offered by
scrubbing by reducing the fresh air
supply. See, for example, ASHRAE
Epidemic Task Force Schools &
Universities, Updated 5-14-2021
(https://tinyurl.com/4fafdyx3).
Especially on the verge of reopening
schools, the latest ASHRAE recommendations
should be checked
while COVID-19 and its variants
still lurk in the buildings and affect
humans.
The second issue that needs
more clarifi cation is the COP of the
ground-source heat pumps used in
this school. Data about COP values
for heating and cooling operations
are not provided. The missing data
raise the question of whether these
heat pumps indeed contribute to
decarbonization in a holistic view,
even if the electricity for driving
the heat pumps is from renewable
energy sources, which in this case is
the solar PV systems.
Of course, heat pumps are energy
effi cient according to the First Law of
Thermodynamics as long as the COP
(including electric power demand
of the circulation pumps between
the heat pump and the geothermal
wells) is greater than one. However,
the First Law does not guarantee
that the heat pump system is environmentally
useful for reducing
the global warming potential in its
proportionate capacity by reducing
CO2 emissions.
The Second Law differentiates that
heat pumps consume electricity
with a unit of useful work potential
of about 0.95 kW/kW and supply (in
heating) or extract heat (in cooling),
which have much lower useful
energy potential, aka exergy.
For example, if in the heating
mode a heat pump provides
hydronic heat to the building
at Tsup of 323 K (50ºC, 581.4ºR),
and returns at Tret of 308 K (35ºC,
554.4ºR), the maximum useful work
obtained is 0.046 kW/kW according
to the ideal Carnot Cycle.
The difference between the two
useful work potentials of electricity
used and heat supplied translates to
nearly avoidable CO2 emissions (by
increasing COP), even if the on-site
PV systems satisfy all the electricity
demand of the heat pumps and their
ancillaries.
The authors should have provided
necessary technical and operational
data to arrive at more conclusive
results. For example, the COP of the
heat pumps they use in the heating
mode should satisfy the following
simple condition:
COP > 0.95 divided by (1 - Tret / Tsup)
Birol Kilkis, Ph.D. Fellow/Life Member ASHRAE,
Ankara, Turkey
The Author Responds
As Dr. Kilkis mentions, the CO2
scrubbers will eventually reach
maximum capacity in a daily operation.
In this application, several
units were installed to provide the
school a full day of operation at
the minimum before reaching this
capacity.
When maximum capacity is met,
the scrubber units close dampers
to the recirculation airstream and
begin a cleaning cycle in which the
excess CO2 and compounds are
vented to the atmosphere. In this
approach, these compounds are
not reintroduced into the school
airstream while the scrubbers are at
max capacity. Carbon capture and
storage (CCS) for use would be ideal
for all captured carbon. However,
CCS is currently only viable at an
industrial scale and is not fi nancially
feasible for a school of this size.
As stated in the article, the ventilation
equipment, ductwork and
airfl ow for the school were not
reduced based on the Standard 62.12010
IAQ Procedure (IAQP) method.
Instead, the design is based on the
Ventilation Rate Procedure (VRP),
which means the ventilation system
does not have reduced capacity or
airfl ow and thus operates with the
code minimum ventilation, even if
the CO2 scrubbers are deactivated
for any reason.
The COPs for the submitted
water-to-air heat pumps vary
based on their capacity. Most units
are between 2 tons and 6 tons in
size, with a minimum submitted
COP of 5.32 to a maximum of 6.44.
Comparing the effi ciency of these
units to alternate HVAC systems
that use energy modeling and data
collecting from the existing installation
determined the geothermal
heat pump system was the most
effi cient system attainable within
the project's budget. These effi ciencies
allowed the low energy use
intensities (EUIs) listed in the article
to achieve Zero Energy certifi cation
with the electricity produced by the
PV panels.
The design team's primary goal
was to reduce the continued energy
S E P T E M B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
9
https://www.tinyurl.com/4fafdyx3 http://www.ashrae.org/

ASHRAE Journal - September 2021

Table of Contents for the Digital Edition of ASHRAE Journal - September 2021

Contents
ASHRAE Journal - September 2021 - Intro
ASHRAE Journal - September 2021 - Cover1
ASHRAE Journal - September 2021 - Cover2
ASHRAE Journal - September 2021 - 1
ASHRAE Journal - September 2021 - Contents
ASHRAE Journal - September 2021 - 3
ASHRAE Journal - September 2021 - 4
ASHRAE Journal - September 2021 - 5
ASHRAE Journal - September 2021 - 6
ASHRAE Journal - September 2021 - 7
ASHRAE Journal - September 2021 - 8
ASHRAE Journal - September 2021 - 9
ASHRAE Journal - September 2021 - 10
ASHRAE Journal - September 2021 - 11
ASHRAE Journal - September 2021 - 12
ASHRAE Journal - September 2021 - 13
ASHRAE Journal - September 2021 - 14
ASHRAE Journal - September 2021 - 15
ASHRAE Journal - September 2021 - 16
ASHRAE Journal - September 2021 - 17
ASHRAE Journal - September 2021 - 18
ASHRAE Journal - September 2021 - 19
ASHRAE Journal - September 2021 - 20
ASHRAE Journal - September 2021 - 21
ASHRAE Journal - September 2021 - 22
ASHRAE Journal - September 2021 - 23
ASHRAE Journal - September 2021 - 24
ASHRAE Journal - September 2021 - 25
ASHRAE Journal - September 2021 - 26
ASHRAE Journal - September 2021 - 27
ASHRAE Journal - September 2021 - 28
ASHRAE Journal - September 2021 - 29
ASHRAE Journal - September 2021 - 30
ASHRAE Journal - September 2021 - 31
ASHRAE Journal - September 2021 - 32
ASHRAE Journal - September 2021 - 33
ASHRAE Journal - September 2021 - 34
ASHRAE Journal - September 2021 - 35
ASHRAE Journal - September 2021 - 36
ASHRAE Journal - September 2021 - 37
ASHRAE Journal - September 2021 - 38
ASHRAE Journal - September 2021 - 39
ASHRAE Journal - September 2021 - 40
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ASHRAE Journal - September 2021 - 49
ASHRAE Journal - September 2021 - 50
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ASHRAE Journal - September 2021 - 60
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ASHRAE Journal - September 2021 - Cover3
ASHRAE Journal - September 2021 - Cover4
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