HVAC in Warehouse

The e-commerce boom in India does not seem to be slowing down – all the big retailers are putting in more money into the business and are expanding their network. With such a large market, majority of which is in the rural sector and untapped, the growth opportunities are immense. The current revenues from the sector are USD 37 billion which is expected to go up to USD 120 billion by 2020. One of the key elements in the e-commerce process chain is the warehouse or ‘fulfilment center’ where products are supplied by manufactures and then distributed to the consumers. These can range from small sheds in crowded markets to large, 1 -2 million square feet warehouse that have multiple levels of stocking and various zones for the multitude of products that are shipped every day.

Warehouses are simple to build and do not have much in terms of complexity by way of machinery, equipment’s etc. and hence one may assume that the HVAC systems of a warehouse are also not very complicated to design and then maintain. If compared to commercial building HVAC systems, warehouses are relatively simpler, but a warehouse brings with its own set of challenges as any design or structure would. HVAC is critical for the warehouses because a lot of products are sensitive to temperature or humidity and dust and no consumer likes to get damaged or defective products.

Typical e-commerce warehouse layout

While most of the space in a warehouse is dedicated to the storage racks, there are other functional aspects that a warehouse must cover. Figure 1 shows a typical layout of a warehouse servicing the e-commerce sector. The main areas, from a HVAC design requirement standpoint are:

The shipping and receiving bays: These are where the delivery trucks get offloaded or loaded with consignments and material. These bays must have the flexibility to allow free movement of the material from inside of the warehouse to the trucks as well as prevent or minimise the untreated and unconditioned air from the outside environment from entering the stowage area.

Stowage areas: This is the main function of a warehouse and is where all the action happens. The stowage racks can vary in height from 3 meter to as high as 10 – 12 meters, with multiple layers of stowage which is accessed by robotic systems. With advances in automation, the height of the stowage racks as well as the warehouse is increasing which poses a challenge for the HVAC designers as they must cater for the right amount of flow rates for such heights. The stowage areas are segregated as per the material and products that are stored. With same day delivery also seeing a lot of demand (Big Basket, Amazon pantry etc.), the warehouse operator looks to maximise the space available and combine the grocery section with the white goods or materials section. This means that the HVAC requirements for these sections will be very different and the design will have to cater for such needs.

Office area: With a typical 1 million square feet sized warehouse having 500 – 600 staff working round the clock, which increase to 1000- 1200 during the peak holiday season, there is a need for an operations team to plan and manage the work flow. There will thus be a dedicated office space in most large warehouses and the HVAC requirements will be that of a typical office environment.

Staff Amenities: Unlike office environments, most staff in e-commerce warehouses are the blue collared workers. They need to be provided with canteen facilities, rest rooms and recreation spaces which will have their own HVAC requirements.

Warehouse Operations: To understand the HVAC requirements of an e-commerce warehouse, one needs to understand the operating cycle of a warehouse. All large warehouses operate 24×7, with the night operations sometimes being the most intensive due to movement of trucks at night. There are usually multiple receiving and dispatch bays which are open to the environment. A large part of the workforce is assigned in packaging the materials that are received, putting on the address labels, putting the items in the boxes and sealing the box before dispatch. There are many machines that are used in a warehouse – Forklift trucks, robotic devices to collect items form the storage bays, cleaning machines, conveyer belts etc. These machines generate heat which needs to be removed by the HVAC system.

HVAC Systems for Warehouses

The key functions of a HVAC system in a warehouse are two-fold – maintaining the ambient air temperature or humidity to the desired levels for staff to work effectively and to maintain the Indoor Air Quality (IAQ) of the space to the acceptable standards. ASHRAE 62.1 2010 lays down the acceptable ventilation rates for warehouses. It is typically 10 cfm/per person but will depend on other factors as well such as outside air quality, type of work etc.

The temperature that is typically maintained in warehouses is around 28 Degrees centigrade with a variance of 1 – 2 degrees. While no humidity standards are defined for warehouses specifically, the design aims for a humidity range of 55 – 65 per cent.

The warehouse HVAC requirements can be segregated to two areas – the stowage section and the non-stowage section. The non-stowage section will cover the office, rest rooms, recreational areas etc.

Stowage Area HVAC: Most warehouses are single storey, big box designs where the stowage racks are positioned. The racks may be 2 – 3-meter-high in smaller warehouses or be as high as 20 meter in large, automated a warehouse. If there are no grocery or perishable items in the warehouse, then the space is only ventilated and not air conditioned. There are three main approaches that designers take to provide ventilation for warehouses

Ceiling fans: The most basic approach is to install ceiling fans across the warehouse stacking zone. These fans circulate the air at a constant rate and help maintain an even temperature across the workspace. The cost of operation is low. However, the fans are not very effective in maintaining the humidity and do not provide enough comfort in peak summers where ambient temperatures are high in the northern plains where a large no of warehouses are set up. This arrangement is suitable for smaller warehouse set ups with low ceiling heights.

Exhaust fans: When the warehouse stores materials that give of fumes or have Volatile Organic Compounds (VOC), then a more effective way to provide good air quality inside the space is to use exhaust fans. These will pull out the indoor air and outside air will enter from the loading bays or other openings. A factor that needs to be considered is that the quality of outside air may not be good so filtration may be needed. Also, exhaust fans have a higher noise level which may impact the staff’s productivity. Another difficulty with exhaust fans is that the air flows get restricted due to the stowage systems which results in hot and cold spots or in adequate ventilation in many areas. Roof mounted, wind turbines are quite popular in warehouses as they have low operating costs and the noise levels are also low.

HVLS Fans: Where the warehouse floor plate is very large and there is enough height, High Volume, Low Speed (HVLS) fans are used. These fans have large radial diameters and provide a column of air downwards as well as outwards which helps circulate the air more effectively than ceiling mounted fans. These fans are also more energy efficient and hence operating costs are low.

Air Washers: Where the ambient temperatures are on the higher side and the products stowed in the warehouse are temperature sensitive, air washers are used. Outside air is passed over cooling pads and through evaporative cooling, the air temperature reduces.

Non-Stowage Area HVAC: The approach to provide HVAC to non-stowage areas in a warehouse is like that of office or recreational space design. Since the spaces are not very large as compared to the warehouse, the typical solution is use of smaller package units.

Conclusion

Ventilation of warehouses is important not only for maintaining desired air quality for the staff working there but also to prevent damage to the products that are stored. E-commerce supply chain relies heavily on good quality warehouses where products can be shipped, sorted for dispatch and stowed for future use. The staff working in warehouses are mostly blue collar but the whole distribution system relies heavily on this staff for stowage, retrieval and packaging of the products and hence, good ventilation of the space is essential. With the requirement of warehouses set to increase exponentially, the need for more advanced ventilation systems will arise and will further help in making the supply chain more effective.