Unique Loads

Designing an HVAC system for a grow facility is inherently different than designing a comfort cooling system for other types of commercial buildings. That’s because the loads in a grow facility are very different than those found in schools, office buildings, or most manufacturing environments.

OPTIMAL ENVIRONMENT: For large grow facilities, chilled water systems make a lot of sense, as they can provide an optimal growing environment for cannabis, while cutting energy consumption. (Courtesy Rex Medlen from Pixabay)

In grow facilities, the plant watering process and the moisture given off by the plants in the transpiration process add a great deal of moisture to the air, so the latent load is significantly higher than in most other types of applications. These applications also experience greater load swings, so the HVAC equipment has to be designed to quickly handle large fluctuations in both sensible and latent loads.

“In a grow facility, when the lights are turned on, most of the sensible load is being applied to the space in an instant, so the system has to immediately catch up with that huge lighting load,” said Brian Rodeghier, vertical market manager at Daikin Applied Americas. “The same thing occurs when the lights go off approximately 12 hours later, and the facility goes from a large sensible load to almost no sensible load.”

There can also be large swings in latent loads, due to the moisture introduced into the space after plants are watered. In addition, the amount of moisture can vary due to the growth cycle, as flowering plants transpire more moisture.

Dealing with abrupt changes in both sensible and latent loads is challenging, which is why HVAC systems designed for comfort cooling in residential/light commercial applications are not recommended for larger grow facilities.

“We recommend using chilled water for cooling and dehumidifying grow facilities and hot water for reheat, so the space is not overcooled during dehumidification,” said Rodeghier.

Numerous Benefits

Chilled water systems offer a number of advantages over other types of HVAC systems, including the flexibility to choose the options that best meet the needs and goals of the grower. That is an important point to consider, especially when comparing chillers to off-the-shelf packaged units, which usually offer limited air handling options. Daikin Applied chillers, for example, can be configured with everything from fully customized air handling units with advanced construction to eliminate sweating, redundant supply fans, and MERV 15 or other types of filters, to smaller, feature-rich fan coils that serve a smaller area.

Energy-saving heat recovery is another reason why growers should consider using chillers in their larger facilities. With this option, chillers extract the heat from the air that is normally rejected outdoors. That heat is then used to make hot water, which is utilized for the reheat process needed for dehumidification. There are a number of free reheat options that can be employed with chillers.

“While some packaged units offer hot gas reheat, they can only dump it back into the airstream from which is was taken,” said Rodeghier. “With a chiller system, heat is pulled out of the whole system and can be put back anywhere it’s needed. There's a lot more ability to move that heat to whichever flower room the grower wants it to go.”

On the air side, heat recovery can be accomplished with a flat plate heat exchanger or with a wrap-around heat pipe. In both cases, these devices can be installed to precool the return air and reheat the supply air all within the air handling unit. Using this option, for example, can reduce the cooling requirements by 35% or more, so instead of a 500-ton chiller plant, only 400 tons may be required. So in addition to saving 100 cooling tons the system produces free reheat needed for the dehumidification process, further reducing (heating) energy needs.

Daikin Applied chillers also offer features that can be of great benefit in the growing number of areas that experience short-term power outages. Thanks to RapidRestore™ and RideThrough™ technology, growers can rest easy, knowing that their crops are protected by equipment that will be back up and running in no time.

“In centrifugal chillers with RideThrough technology, if the power comes back on within 17 seconds, it will pick back up where it left off when the power died,” said Rodeghier. “It will literally be less than a minute before the grower has chilled water again. If there is a longer power delay, then the chiller can restart as fast as 20 seconds after power is restored, and within 75 seconds, the facility will have 80% of the cooling capacity. Compare that to packaged equipment, which often has to stay off for at least 15 minutes after a power outage.”

Another advantage of using a hydronic system is that it is very easy to add redundancy. With packaged equipment, for example, a typical grow room may be served by only one unit, and there is no backup should that unit fail or need to be serviced. With a hydronic system, multiple air handling units are usually used in a zone, and the only components that may need to be replaced are the supply fan or control valve. Both parts are easy to keep in stock.

“If a chiller goes down, that can be a problem, but multiple chillers are usually serving a facility,” said Rodeghier. “For example, in a 500-ton system, a grower could have two 250-ton chillers installed, and a third could be used as backup in case one goes down. That way, the grower always has 500 tons available, because the chillers feed all the grow rooms. Redundancy is a lot easier with a hydronic system.”

Peace Of Mind

While chilled water systems can provide a number of benefits for growers, one of the biggest may just be peace of mind. Reliability is key with growers, because if their HVAC system fails or is inoperable for just a few hours, their entire crop may suffer. And the system not only needs to run, it needs to maintain the necessary temperature and humidity conditions required for optimal plant growth. Daikin Applied chillers are installed in dozens of grow facilities around the country, so they have a proven track record in the industry.

“Not every grower can install a chilled water system, especially if they don’t have the space for the equipment or the CAPEX budget to invest in a chilled water system up front,” said Rodeghier. “But if we have the opportunity to talk to growers about the advantages of chilled water systems, we certainly do. They really are the system of choice for larger grow facilities. And we do see grow facilities that made the cost-based decision to avoid chilled water on their first design, embrace this approach on future projects. Some have learned the hard way.”