INTRODUCTIONStratification is the physical occurrence of an increasing air temperature gradient betw...

1. Cold weather destratification energy savings of a
warehousing facility.
INTRODUCTION
Stratification is the physical occurrence of an increasing air
temperature gradient between the floor and the ceiling,
usually due to uncirculated or stagnant air near the ceiling
(Pignet and Saxena, 2002). Pignet et al. (2002) also state
that the heating requirements of a facility are increased where stratification is present due to
increased average wall and ceiling temperatures. Aynsley (2005) presents several different methods
of estimating energy savings in warehouse applications including; using the different heat losses
through the roof, at the two temperature differences with and without destratification, using an
energy balance of the building including heat from other sources as well as roof temperature
differences, and using a temperature profile from floor to ceiling to calculate the average indoor air
temperature. Andersen (1998) presents sample vertical heat profiles dependent on how heat is
supplied and mixed within a room. Aynsley (2005) presents a case study that shows a 26.4%
reduction in gas use due to destratification in a shipping and receiving warehouse.
Large diameter fans are being used in warehouse applications to provide destratification of vertical
air temperatures for cold weather energy savings. An evaluation of environmental conditions and
energy savings using large diameter fans in a commercial manufacturing and warehousing
application in the Toronto area was completed during the winter/spring of 2008. The fans were
originally installed to increase employee comfort by providing a cooling effect during hot weather in
the summer period. The fans were not being used during cold weather due to a lack of
understanding of potential benefits. This evaluation quantified the energy savings from
destratification for the facility operators and provided a better understanding of the benefits of fan
operation during the heating season.
METHODOLOGY
Five, 20 ft (6.91 m) diameter, 1.0 hp fans were installed in a combined manufacturing and
warehouse facility in the Toronto, Canada area. The entire manufacturing/warehouse area is
approximately 92,500 [ft.sup.2] (8,600 [m.sup.2]). Fans had been strategically located to provide
occupant cooling benefit in the manufacturing area of the facility. A layout of the facility with
heating, monitoring and destratification fan locations is shown in Figure 1.

2. [FIGURE 1 OMITTED]
Heater Operation
Heating is provided by 18 forced air unit heaters with 16 heaters each having inputs of 165,000
Btu/hr (48.34 kW) and 2 heaters each having inputs of 250,000 Btu/hr (73.25 kW). The timed
operation of each heater was monitored using a relay connected to the thermostat. A data logger
was installed on each thermostat/relay to record operating times of the heaters.
Temperature Monitoring
Five temperature profiles were monitored throughout the warehouse area. Each of the profiles
included 6 temperature sensors placed from the floor to ceiling at 0 ft, 5 ft (1.52 m), 9 ft (2.74 m), 15
ft (4.57 m), 21 ft (6.4 m), and 27.5 ft (8.38 m) heights. Profile #1 and Profile #2 also had a sensor
located at the 24 ft (7.32 m) height. A section view of the temperature profile locations is shown in
Figure 2. Temperature sensors were taped to a post at each profile location and sensor wire was run
down the post to a datalogger. Temperature data was recorded at 10 minute intervals.
[FIGURE 2 OMITTED]
Dates and Operation
The test approach was to have destratification fans operating for a one week period, then off for
alternate one week periods. Evaluation began on 25-Feb-08 with monitoring and weekly on/off fan
operation continuing until the end of March 2008. Data was downloaded from monitoring equipment
on a weekly basis.
Initially the fans were operated at 20Hz in the reverse direction to direct air toward the ceiling. This
was done to reduce the airspeed at floor level due to occupant concerns. On 17-Mar-08 the fans
were tested and operated in the forward direction at 15Hz. Having minimal occupant concerns the
fans operated in this fashion for the remainder of the test. Fan #5 was an exception as its speed was
reduced to 11Hz to prevent light-weighted manufacturing material from being disturbed.
RESULTS
Air Temperature
The air temperatures measured at Profile #3 are shown in Figures 3a and 3b. This location was
approximately 29 ft (8.839 m) from the centre of the closest large diameter fan. Being the closest,
Profile #3 had the most significant temperature response to the destratification fans. The air

3. temperatures at the 9 ft (2.74 m) height have been removed from Figures 3a and 3b for clarity.
[FIGURE 3 OMITTED]
Reverse Direction
The period noted as [UP] on the temperature figures indicates the fans operating in the reverse
direction and directing air toward the ceiling. Table 1 indicates the temperature differences versus
when the fans were not operating. These temperatures are read directly from Figures 3a and 3b.
Table 1. Temperature Change (Reverse Direction)
Height, m (ft) Temperature Change vs No Fans, [degrees]C
([degrees]F)
Ceiling, 8.38 (27.5) -3.5 (-6.3)
7.32 (21) -1.0 (-1.8)
4.57 (15) +1.0 variable (1. 8)
2.74 (9) +0.75 variable (1.35)
Thermostat, 1.52 (5) +0.5 variable (0.9)
Floor, 0 +0.5 variable (0.9)
Forward Direction
The period noted as [DOWN] on the temperature figures indicates the fans operating in the forward
direction and blowing air toward the floor. Table 2 indicates the temperature differences versus
when the fans were not operating. These temperatures are read directly from Figures 3a and 3b.
Table 2. Temperature Change (Forward Direction)
Height, m (ft) Temperature Change vs No Fans, [degrees]C
([degrees]F)
Ceiling, 8.38 (27.5) -4.0 (7.2)
7.32 (21) -1.5 (-2.7)
4.57 (15) 0.0 (0.0)

4. 2.74 (9) +0.5 (0.9)
Thermostat, 1.52 (5) +1.0 (1.8)
Floor, 0 +1.5 (2.7)
Operating the fans in the forward direction further reduced the temperature stratification versus
operating fans in the reverse direction. A total temperature profile difference of less than
0.5[degrees]C (0.9[degrees]F) was achievable with the fans in the forward direction as shown in
Figures 4a and 4b.
[FIGURE 4 OMITTED]
Gas Use
A summary of the operation and gas use for the test period is provided in Table 3. The Hours of Test
for the Fans ON period is a combination of the fans operating in both the reverse/forward (144/192
hrs) directions. The gas use of the facility was analyzed on an hourly Gas Use per Degree basis
whereas the Degree Temperature Difference indicates the difference between inside and outside
temperatures. A savings of 19.3% was achieved through the use of the destratification fans.
Calculated values were done using SI units and converted.
Table 3. Summary Gas Use
Fans ON Fans OFF
Hours of Test, hours 336 287
Heater Op Time, hours 1,228 1,307
Gas Use, therm, [m.sup.3] ([ft.sup.3]) 6,082 6,402
(2,147) (2,260)
Average Outside Temperature, [degrees]C -2.9 (26.8) -3.4 (25.9)
([degrees]F)
Average Inside Temperature, [degrees]C 23.2 (73.8) 22.7 (72.9)
([degrees]F)
[Thermostat Level]
Degree Temperature Difference, 26.1 (47) 26.1 (47)
[degrees]C ([degrees]F)
Gas Use per Degree, [m.sup.3]/hr * 0.692 0.857
[degrees]C (therm/hr * [degrees]F) (0.136) (0.168)

5. Gas Savings, [ft.sup.3]/hr * [degrees]F 0.165
[= 0.168 - 0.136] ([m.sup.3] /hr * (0.032)
[degrees]C [= 0.857 - 0.692])
Gas Savings (%) 19.3%
Annual Gas Savings @ 4065 HDD, [m.sup.3] 16,097
(@ 7317 HDD, therm) (5,682)
The Annual Gas Savings was calculated using the 30 year, <18[degrees]C (<65[degrees]F), heating
degree days of 4065[degrees]C (7317[degrees]F) for Toronto, Canada (Environment Canada, 1971-
2000). This is calculated as shown in Equation (1) below (ASHRAE 2005).
[GasSave.sub.Annual] = [GasSavings.sub.Hourly] x HDD x 24 (1)
where:
[GasSave.sub.Annual] = the annual gas savings, [m.sup.3] ([ft.sup.3])
[GasSavings.sub.Hourly] = the hourly gas savings, 0.032 [m.sup.3]/hr*[degrees]C (0.165
[ft.sup.3]/hr*[degrees]F)
HDD = the 30 year, <18[degrees]C (<65[degrees]F), heating degree days
24 = conversion of daily to hourly time period, hrs/day
Fan Motor Electrical Use
The fan motor electrical consumption was calculated using a VFD simulation software program. It
was not measured on site. Input and calculated parameters for the simulation are included in Table
4 on a per fan basis.
Table 4. Fan Motor Electrical Consumption
Input Parameter Value
Actual Nameplate HP 1.0
Motor Loading (%) 85%
Motor Efficiency (%) 80%
VFD Efficiency (%) 97%
Airflow (%) * 30%

6. Output Parameter Value
Effective Nameplate HP 0.14
Annual Electrical Consumption (kWh/yr) 593
* The percentage of airflow was estimated as the airflow (rounded up to
the nearest 10%) resulting from operating the fans at 15Hz.
The five fan motors were calculated to consume 2,965 kWh during the heating season which, at an
average blended electricity price of $0.11/kWh, required $326 in operating costs.
DISCUSSION
The gas use savings are determined throughout the entire monitoring period. This included periods
when the fans were operating in both the forward and reverse directions. Reviewing the
temperature profiles during these periods suggest that better destratification was achieved when
the fans were operating in the forward direction. This would suggest that these gas savings values
should be considered conservative versus fans solely operating in the forward or down direction. The
ability to operate the fans in either the forward or reverse direction will somewhat depend on local
facility conditions and occupancy comfort. As was the case at the test facility, the initial request to
operate the fans in the reverse direction was largely based on occupant perception of the fans
providing cooling instead of increasing floor temperatures. Once the fans were tested in the forward
direction the occupants had a better understanding of the environmental benefits created by the
fans. Many warehouse applications have very low occupancy and should not have an issue operating
fans in the forward direction.
The five destratification fans provided an annual natural gas savings of 16,097 [m.sup.3] (5682
therm). Using a natural gas rate of $0.40/[m.sup.3] ($1.13/therm) provides a natural gas dollar
savings of approximately $6440.
This study focussed on determining the energy savings due to temperature destratification in a
commercial warehouse. Throughout the course of this study the various temperature profiles
suggested that each fan had a destratification influence of about 30.5 m (100 ft) diameter or 730
[m.sup.2] (7854 [ft.sup.2]). This was demonstrated due to the fact that a small temperature influence
was shown at Profile #2. These temperatures were 18.3 m (60 ft) away from the centre of the
nearest fan. The total area of destratification coverage for the five fans using the suggested
influence is about 3650 [m.sup.2] (39,250 [ft.sup.2]). This coverage represents approximately 42% of
the entire building. If the building were to have complete destratification coverage then the
potential annual gas savings would be 45.9% (19.3% divided by 42%) or 38,326 [m.sup.3] (13,529
therm). This would also suggest that each fan provides nearly 45.9% savings for its own area of
destratification. It is important when estimating energy savings to consider the percentage of total
building coverage provided by the destratification fans. This area of influence should be considered
as a starting point for design considerations understanding the limitations upon which it is based
and the fact that it was not the primary focus of the study. This particular application required
conservative fan speeds to prevent fabric material from being disturbed. It is reasonable to assume
that changes to factors including; ceiling height, fan diameter and fan speed may affect the area of

7. influence.
The electrical consumption of 2965 kWh or $326 to operate the five fan motors represents a
parasitic loss of approximately 5% of total cost savings ($326/$6440). It is logical to suggest that a
portion of the parasitic losses are offset by electrical savings through the reduced use of auxiliary
heating equipment such as blower motors on space heating equipment.
The increase in thermostat and floor level temperatures of 1.0[degrees]C (1.8[degrees]F) and
1.5[degrees]C (2.7[degrees]F) respectively due to temperature destratification suggest a decrease in
thermostat settings by this amount may be possible while maintaining occupancy comfort. Further
gas savings may be possible with adjustments or recalibration of thermostat settings.
SUMMARY
The use of destratification fans during cold weather reduced ceiling temperatures by 4.0[degrees]C
(7.2[degrees]F) and increased floor temperatures by 1.5[degrees]C (2.7[degrees]F) in a
manufacturing and warehouse facility in the Toronto, Canada area. Operating the fans in the
forward or downward direction provided improved temperature destratification versus operating
fans in the reverse direction. A total temperature profile difference of less than 0.5[degrees]C
(0.9[degrees]F) was achieved with the fans in the forward direction. Use of the destratification fans
provided an average gas savings of 19.3% of the entire warehouse consumption. Monitoring and
evaluation included periods when the fans were operated in both the forward and reverse directions.
It is suggested that gas savings could have been even higher if the fans had operated solely in the
forward or downward direction.
The five destratification fans provided an annual natural gas savings of 16,097 [m.sup.3] (5682
therm). Using a natural gas rate of $0.40/[m.sup.3] ($1.13/therm) provides a natural gas dollar
savings of approximately $6440.
Interpretation of the results by the author suggests that each fan provides an influence of
destratification of about 30.5 m (100 ft) diameter or 730 [m.sup.2] (7854 [ft.sup.2]). This would also
suggest that each fan provides nearly 45.9% savings for its own area of destratification. This area of
influence should be considered as a starting point for design considerations understanding the
limitations upon which it is based and the fact that it was not the primary focus of the study.
The electrical consumption of 2,965 kWh or $326 to operate the five fan motors represents a
parasitic loss of approximately 5% of total cost savings ($326/$6440). It is logical to suggest that a
portion of the parasitic losses are offset by electrical savings through the reduced use of auxiliary
heating equipment such as blower motors on space heating equipment.
ACKNOWLEDGMENTS

8. The authors would like to thank:
* Enbridge Gas Distribution for monitoring and evaluation funding.
* Hunter Douglas Canada for providing the facility and support personnel.
* Envira-North Systems Ltd. for equipment technical support and financial assistance.
REFERENCES
Andersen, K.T. 1998. Design of natural ventilation by thermal buoyancy with temperature
stratification. Proceedings of 6th International Conference on Air Distribution in Rooms,
ROOMVENT'98, 2:437-444.
ASHRAE. 2005. 2005 ASHRAE Handbook--Fundamentals, p.32.18. Atlanta: American Society of
Heating, Refrigerating and Air-Conditioning Engineers, Inc.
Aynsley, R. 2005. Saving heating costs in warehouses. ASHRAE Journal 47(12): 46-51.
Pignet, T. and U. Saxena. 2002. Estimation of energy savings due to destratification of air in plants.
Energy Engineering 99(1):69-72.
Environment Canada, 1971-2000. Canadian Climate Normals.
Mark Armstrong, PEng, PE
Member ASHRAE
Bill Chihata, PEng
Associate Member ASHRAE
Ron MacDonald, PEng
Member ASHRAE

9. Ron MacDonald is president and Mark Armstrong is an engineer at Agviro Inc. consulting engineers,
Guelph, Ontario, Canada. Bill Chihata is the commercial sector program manager for Enbridge Gas
Distribution Inc., North York, Ontario, Canada.
COPYRIGHT 2009 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
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