Staff
Analysis for Declaratory Statement Request
DS 2015-154
Issue: Petitioner seeks a Declaratory Statement on an
interpretation of Section C403.2.6 energy recovery ventilation systems. Chapter
4 of the 5th Edition (2014) Florida Building Code, Energy Conservation,
Section C403.2.6. Specifically, requesting clarification of Exception C403.2.6
(7) and a determination on a type of product as it relates to this exception.
Background:
The Petitioner, David A. John, Stan Weaver
& Company, seeks a determination on a type of product as it relates to
Exception 7 of Section C403.2.6 of the Florida Building Code 2014, Energy Conservation.
Stan Weaver & Company is a manufacturer’s representative of
air distribution products for central Florida. One of the manufacturers they
represent is Heat Pipe Technology (HPT) who manufactures heat pipes that
are used in air handler units as an energy savings device.
The petitioner feels that
having a heat pipe included as an exception in C403.2.6
Energy recovery ventilation systems is a major point of emphasis with Florida
engineers and owners. It allows engineers to design HVAC systems, include a
heat pipe, and not have to provide an additional energy recovery system. The
petitioner feels it will save the building owner the expense of two heat
recovery systems. Below are the relevant circumstances.
A selection and payback analysis for a
current design under consideration
·
100% OA unit with constant 20,000
CFM
·
52 F off the cooling coil
·
no more than 65 F supplied
after reheat
·
supplemental reheat is via hot water
Assumptions:
·
Chiller has
efficiency of 20 EER
(or 0.600 kW/ton)
·
utility rate is $0.10/kWh
·
hot water costs $1/therm (therm = 100,000 Btu’s)
·
AHU
fan
is 70% efficient and motor
is
90% efficient
·
Temperatures and hours based on Tampa
bin
data for one year
·
AHU
operates 24/7/365
At the first/uppermost bin (where OA
is
between 90 F and
95
F)…
Cooling Savings = Tons removed X Chiller’s
kW/ton X Tampa’s cooling hours X Utility Rate
= 22 tons
x 0.600 kW/ton x 157 Hours x $0.10/kWh = $209
Heating Savings = Free Reheat X Utility Rate … Free Reheat = 265,746 BTUH = 2.66 Therms/hour = 2.66 Therms/hour X $1/Therm X 157 Hours = $417
Fan Penalty = (Airflow X Total Static Pressure X Utility Rate X Hours) / (Constant X Fan & Motor
Efficiencies)
= (20,000 CFM X 0.37” X $0.10/kWh X 157 hours) / (8,522 X 0.7 X 0.9)
= $22
NET Savings (for 90F-95F bin) = $209 + $417 - $22
= $604
Then calculate for
each bin and sum to
get
NET Annual Savings
= $16,965*
* See attached Bin
Analysis for breakdown.
If
this standard 2-row DHP is budgeted
for $25,000 and annual savings
are
$16,965…
Payback is less than
a year and a half
Question: If an air handling unit is provided with a
wrap-around heat pipe (for
dehumidification), is it acceptable to not provide an
Energy Recovery Ventilation System per paragraph C403.2.6.7?
Petitioner
respectfully believes the answer to the question outlined above is yes, if a
wrap-around heat pipe coil is used, it is acceptable to not provide an Energy
Recovery Ventilation System per paragraph C403.2. A wrap-around heat pipe is
commonly viewed as a dehumidification device that employs energy recovery in
series with the cooling coil.
-----
Reference Material
Florida Building Code 5th
Edition (2014), Energy Conservation
Chapter
4
C403.2.6
Energy recovery ventilation systems. Where the supply airflow rate of a fan system
exceeds the values specified in Table C403.2.6, the system shall include an
energy recovery system. The energy recovery system shall have the capability to
provide a change in the enthalpy of the outdoor air supply of not less than 50
percent of the difference between the outdoor air and return air enthalpies, at
design conditions. Where an air economizer is required, the energy recovery
system shall include a bypass or controls which permit operation of the
economizer as required by Section C403.4
Exception: An energy recovery ventilation system shall not be required
in any of the following conditions:
1. Where energy recovery systems are prohibited by the Florida Building
Code, Mechanical.
2. Laboratory fume hood systems that include at least one of the following
features:
2.1. Variable-air-volume hood exhaust and room supply systems capable of reducing
exhaust and makeup air volume to 50 percent or less of design values.
2.2. Direct makeup (auxiliary) air supply equal to at least 75 percent of the
exhaust rate, heated no warmer than 2°F (1.1°C) above room set point, cooled to
no cooler than 3°F (1.7°C) below room set point, no humidification added, and
no simultaneous heating and cooling used for dehumidification control.
3. Systems serving spaces that are heated to less than 60°F (15.5°C) and are
not cooled.
4. Where more than 60 percent of the outdoor heating energy is provided from
site-recovered or site solar energy.
5. Heating energy recovery in Climate Zones 1 and 2.
6. Cooling energy recovery in Climate Zones 3C, 4C, 5B, 5C, 6B, 7 and 8.
7. Systems requiring
dehumidification that employ energy recovery in series with the cooling coil.
8. Where the largest source of air exhausted at a single location at the
building exterior is less than 75 percent of the design outdoor air flow
rate.
9. Systems expected to operate less than 20 hours per week at the outdoor
air percentage covered by Table C403.2.6.
TABLE C403.2.6 ENERGY RECOVERY REQUIREMENT
|
CLIMATE ZONE |
PERCENT (%) OUTDOOR AIR AT FULL DESIGN AIRFLOW RATE |
|||||
|
≥ 30% and < 40% |
≥ 40% and < 50% |
≥ 50% and < 60% |
≥ 60% and < 70% |
≥ 70% and < 80% |
≥ 80% |
|
|
DESIGN SUPPLY FAN AIRFLOW RATE (cfm) |
||||||
|
3B, 3C, 4B, 4C, 5B |
NR |
NR |
NR |
NR |
≥ 5000 |
≥ 5000 |
|
1B, 2B, 5C |
NR |
NR |
≥ 26000 |
≥ 12000 |
≥ 5000 |
≥ 4000 |
|
6B |
≥ 11000 |
≥ 5500 |
≥ 4500 |
≥ 3500 |
≥ 2500 |
≥ 1500 |
|
1A, 2A, 3A, 4A, 5A, 6A |
≥ 5500 |
≥ 4500 |
≥ 3500 |
≥ 2000 |
≥ 1000 |
> 0 |
|
7, 8 |
≥ 2500 |
≥ 1000 |
> 0 |
> 0 |
> 0 |
> 0 |
|
NR = not required |
ASHRAE 90.1-2010 User’s Manual.
Energy Recovery (6.5.6)
Exhaust Air Energy Recovery (6.5.6.1)
The requirements for exhaust air energy recovery
have been significantly increased in stringency in the 2010 Standard. The
standard requires exhaust air energy recovery on individual fan systems that
meet or exceed the criteria in Table 6-E (Table 6.5.6.1 of the Standard). The
requirements are based on climate zone, percent outside air at design condition
and the design supply flow airflow rate.
Equipment used to meet this requirement includes plate heat exchangers (plastic
and metal), heat pipes, run-around coils and enthalpy wheels, but which
must also meet the recovery effectiveness discussed below.
The standard
defines exhaust air energy recovery as the process of exchanging heat (sensible
and/or latent) between the exhaust and outdoor airstreams. This reduces
energy usage in the following manner:
-
During periods of heating, the exhaust air can
preheat the cool outdoor air through sensible (dry) exchange.
-
During periods of cooling, the exhaust air can
precool the hot outdoor air through sensible (dry) exchange.
-
During periods of cooling, dry exhaust air can be
used to dehumidify moist outdoor are through latent exchange.
-
During periods of heating, exhaust air can be used
to humidify dry outdoor air through latent exchange.
Exceptions to 6.5.6.1
There are a number of exceptions to the requirement
for exhaust air energy recovery systems:
I) Systems requiring dehumidification that employ energy recover in series
with the cooling coil. This exception recognizes the energy savings inherent in
series energy dehumidification systems.
INTERPRETATION IC 90.1-2004-3 OF ANSI/ASHRAE/IESNA STANDARD
90.1-2004
Energy Standard for
Buildings Except Low-Rise Residential Buildings
©2006
Interpretation: Exception (i) to Section
6.5.6.1 allows the use of dehumidification devices for ventilation air streams,
provided that the system requires dehumidification, and provided that the system
uses energy recovery in series with the cooling coil.
A system which uses a
desiccant-assisted cooling coil is also allowed under exception (i), provided
that all of the energy it uses for desiccant reactivation is recovered from
within that same system.
Question: Is this interpretation
correct?
Answer:
Yes, your interpretation is
correct and the desiccant wheel with regeneration obtained from site recovered
heat which in your design is from the refrigeration condenser will meet the requirements
of exception 6.5.6.1 (i). It should also be noted that there are other means for recovering heat like the
heat pipe system shown in your diagram as well as condenser heat rejection
coils placed downstream from a conventional evaporator coil.
Staff Analysis
Question: If an air handling unit is
provided with a wrap-around heat pipe (for
dehumidification), is it
acceptable to not provide an Energy Recovery Ventilation System per paragraph
C403.2.6.7?
Answer:
Option #1/Petitioner:
Petitioner respectfully believes the answer
to the question outlined above is yes, if a wrap-around heat pipe coil is used,
it is acceptable to not provide an Energy Recovery Ventilation System per
paragraph C403.2. A wrap-around heat pipe is commonly viewed as a
dehumidification device that employs energy recovery in series with the cooling
coil.
Option #2/Staff:
No, the wrap-around heat pipe in question is not configured to provide heat exchange (sensible and/or latent) between the exhaust and outdoor airstreams and therefore, it does not fall within the technical scope of Section C403.2.6, Exception 7 of the 5th Edition (2014) FBC, Energy Conservation.