By Abtar Singh, President – Singh360  Inc.

When it comes to reducing energy in supermarkets, we either focus on refrigeration (because it consumes 40-50% of the total energy) or lighting (which is pretty easy to understand).  However, HVAC equipments (almost 20% of the store power) are often overlooked though they can significantly impact energy consumption, provide customer comfort for better shopping experience and reduce food product quality and shrinkage.

So what are the ways HVAC energy consumption can be reduced in a retail environment? Here’s a roundup of the important ideas to consider in your store:

1)      Store Pressure. Negative pressure encourages leakage of the unconditioned air from the outside. Maintaining the store under a positive pressure eliminates the introduction of outside air into the building. Moreover, besides causing thermal discomfort, air infiltration may also lead to the buildup of humidity that has a negative impact on refrigeration performance (longer defrost and higher door heater consumptions).

2)      Optimum Make up Air. In order to reduce the need of heating or cooling, the fresh air intake in the building can be regulated. This is done via Demand Control Ventilation (DCV) strategy.  DCV allows the regulation of ventilation based on the amount of CO2 level in the building at a particular time. Energy is saved not only because air distribution is lessened but also because lesser air is heated or cooled.  It should also be noted that some retailers have cleaning chemicals, plants and apparels that exhale CO2, and hence the CO2 sensor can give false readings. Therefore, the location of a CO2 sensor and alternative strategy becomes important.

3)      Free Cooling. (Also called economizer strategy.)  During cooler days, the air can be just brought in without any conditioning.  Traditional enthalpy method may not be suitable for supermarkets due to cold air spillage from refrigeration units in the store.  Depending on the type of cases (open, doors etc.) and air pattern, the free cooling (economizer) strategy will have to be fine-tuned for a supermarket.

4)      Un-occupied Settings. If the store is not trading 24 x 7 or there are certain zones that are un-occupied during certain times of the day, the easiest way to save energy is to raise the cooling set point from 72F to 78F and lower the heating set-point from 70F to 66 F during an un-occupied period.  If one does not have a building management system (BMS), then plan spending $200 on a programmable thermostat.  This will definitely provide quicker payback.

5)      Humidity Control. Humidity control is an important factor in controlling the energy consumption in a supermarket. HVAC has an EER (Energy Efficiency Ratio) of 10 and refrigeration has an EER of about 4.  Hence, it is more economical to de-humidify using a HVAC system rather than to create frost in the refrigeration coils & doors.  However, one has to watch out for the reheat strategy when de-humidifying the store.  Lower humidity is always not best for the produce and hence food quality plays a role in deciding the optimum control strategy.

6)      Zone Separation. Zoning reduces the area you need to heat & cool. Zoning allows de-centralization of control and allows each zone to have a temperature independent of the other and a temperature which is required for that zone without affecting the other. Ensure that your conditioned zones (typically the sales floor) are physically separated from the un-conditioned zones (typically the back room).

7)      Sensor Calibration. Humidity and temperature sensors that control the HVAC unit should be calibrated periodically.  Even a small error in the percentage of calibration can cause the HVAC unit to provide a less optimum environment for the store.

8)      Variable Speed Drives (VSD): VFD or VSD on fan blowers is a useful energy saving strategy.  One should regulate the motor speed according to the cooling demand requirement. Since power is equal to the cube of speed, when the speed is reduced the power consumption will also reduce, hence allowing a reduction in energy consumption.

9)      Component Performance. Check performance of key components such as compressors, condensers, evaporators, TXV, furnace & filters.  This should be a part of the planned preventative maintenance schedule.

10)  Digital Thermostat or EMS Retrofits. If the HVAC unit is on mechanical control, a computer based controller can provide quick payback.  Automatic control can be used for occupancy schedule and remote diagnostics.

11)  HVAC Test and Balance: Air testing and balancing is required to adjust the amount of air distribution in a given HVAC zone. The amount of air that is required to be supplied to each conditioned zone is the amount required to balance the given gain (or loss) of heat in that particular area.

12)  Replacing Older Units with Energy Efficient Units: Replacing older, inefficient heating and air-conditioning units with more modern and efficient units can save substantial money. Besides, new units typically are much more reliable and can reduce maintenance cost as well.  Specification of size, weight, energy costs should be kept in mind while choosing a new unit. The heat from the units condensers can also be reclaimed and utilised for re-heating (de-humidification).

13)  Avoid Simultaneous Heat & Cool: Many a times, either controls are improperly set or the design of the HVAC system within a supermarket is such that while one RTU is in the cooling mode, the other RTU within the same zone is in the heating mode.  This can cause a huge wastage of energy.  A proper retro-commissioning of the store can unearth such flaws.

14)  Reheat using Refrigeration Condenser Load: A refrigeration system within a supermarket can have a huge condenser heat available that can be used in the reheat stage during de-humidification.  Typically, dehumidification is required during summer when significant refrigeration condenser heat is available. This will help in supplying fresh air at lower dew-point and higher dry-bulb temperature, which is important for better refrigeration equipment (defrost and door heater) performance.

15)  Heat Reclaim Strategy: Refrigeration condenser heat within supermarkets can be reclaimed to heat the building in winter.  This is not always the best strategy because it increases the refrigerant charge and potential for refrigerant leaks.  However, depending on the logistics, store size and zone, it may be worth considering.  However, one has to be careful that the heat reclaim strategy does require condensers to run at higher head pressure (increased compressor power); though it is usually cheaper than heating using electric heaters or natural gas.  However, in some states natural gas is cheaper than electric and hence it may not be cost effective to heat the building using condenser heat.

16)  Retro-commissioning: It is well documented that retro-commissioning identifies maintenance issues, improves equipment performance and saves 10-15% energy. Retro-commissioning is a systematic process of assuring that a building performs in accordance with the design intent and the owner’s operational needs. The goal is also to achieve energy savings by ensuring that all included systems are operating at an optimum level of performance.

What Energy Idea do you think matter most to you? Leave a comment and give us your take.