ASHRAE Journal - December 2021 - 10

LETTERS
Solving the
Large Building
All-Electric
Heating Problem
Regarding October's " Solving the
Large Building All-Electric Heating
Problem " by Brandon Gill, P.E.,
Member ASHRAE, I'd like to know
what Mr. Gill thinks about:
The practical (smallest) building
size (or other criteria) for which the
time-independent energy recovery
(TIER) system is applicable.
* The best strategy for selecting/
sizing components. I could imagine
some trial and error, perhaps using
an energy model?
* Whether it's practical to model
such a system with available software
such as EnergyPlus with or
without a lot of scripting?
* How to provide clear BAS sequences
of operation for contractors
not likely to be familiar with such a
complex system.
* The best way to guide commissioning
agents as they test the
system.
* The best methods for ensuring
building operator success as they
observe and maintain such a system.
Thanks for the thoughtful article!
James V. Dirkes II, P.E., Life Member ASHRAE,
Grand Rapids, Mich.
The Author Responds
The reader poses several good
questions. Responding in order:
* We have considered applying the
time-independent energy recovery
(TIER) concept in buildings as small
as roughly 100,000 ft2 under unique
circumstances, but 150,000 ft2 or
200,000 ft2 is probably a more reasonable
cutoff for most applications.
10
Essentially, when a building is large
enough that a chilled water plant is
under consideration in lieu of direct
expansion systems, TIER may be
viable.
* The trickiest design aspect is
appropriately sizing the thermal
energy storage tank and trim heat
source, which is generally air-towater
heat pumps in all-electric
designs. This requires a design
heating day 24-hour load profile for
both heating and cooling-extracted
from load calculation software or
other modeling software-so that the
heat recovery, storage and trim heating
dynamics can be appropriately
modeled.
With known load profiles and projected
equipment efficiencies, the
amount of trim heat can be manipulated
to determine the required
tank size. As noted in the article, we
generally try to maximize tank size
subject to architectural constraints
to minimize cost and maximize
efficiency.
* I am not an EnergyPlus expert,
so I cannot state definitively whether
modeling condenser water TIER
is possible or not with extensive
scripting. I can state, however, that
it is likely to be quite difficult. Thus
far we have developed " Exceptional
Calculations " for code compliance
using detailed spreadsheet models
to capture plant dynamics. Load and
weather data outputs from compliance
software are fed into these
models allowing for 8,760 hourly
energy calculations. These spreadsheets
use the same multivariate
regression curve models for chillers,
towers, etc., as EnergyPlus to
produce defensible results.
* Thorough, well-written sequences
of operation are undoubtASHRAE
JOURNAL ashrae.o rg D ECEM BER 2 0 2 1
edly required to ensure that a
complex TIER system operates to
its fullest potential. We recommend
writing sequences of operation in
the style of ASHRAE Guideline 36 to
clearly convey design intent. The designer
must be well versed in control
theory and understand plant equipment
dynamics to do this well.
* Hopefully, we will have a better
opportunity to address commissioning
in a follow-up lessons learned
article. We will be commissioning
a couple TIER systems in the near
term.
* Training, training and more
training are required to ensure that
building operators understand the
design intent and system dynamics
since they are not necessarily intuitive,
nor obvious.
Brandon Gill, P.E., Member ASHRAE, Alameda, Calif.
Errata
In November's " A Bipolar
Ionization Primer for HVAC
Professionals " by David N. Schurk,
Member ASHRAE, guidance from
the CDC was incorrectly attributed
to ASHRAE.
In addition, a sentence in that
paragraph contained a typo. The
corrected sentence is " Consumers
should request efficacy performance
data that quantitatively demonstrates
a clear protective benefit
under conditions consistent with
those for which the consumer is
intending to apply the technology. "
ASHRAE Journal regrets the error.
Logged in ASHRAE members can
download the updated article here:
https://tinyurl.com/vxmvx9ck
https://www.tinyurl.com/vxmvx9ck https://www.ashrae.org/
ASHRAE Journal - December 2021

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