November 2017, Volume 24    

By Brad Tully - Vice President and General Manager, Price Mechanical DOWNLOAD ARTICLE

The indoor environment is the single most important factor for maximizing plant transpiration, which leads to maximized crop growth potential and harvest yield. The Price GRW is purpose built for indoor horticultural applications to provide the environmental control necessary for producing superior crop yields at low operating and life cycle costs. In addition, the GRW unit limits the introduction of harmful contaminants and ultimately prevents the risk of crop failure.

This application-specific unit is based on our proven SolutionAir technology, which has been used in applications including laboratories, archives and pharmaceutical manufacturing. Traditional HVAC cannot match the performance, controllability or reliability of the GRW when operated in horticultural environment conditions.

Figure 1: Price GRW vs Traditional HVAC

The Price GRW is designed to manage the large transient changes in sensible and latent loads that are generated by the plant’s varying circadian light and watering cycles.

These swings in humidity and temperature need to be controlled independently to provide the ideal growing environment. This results in space conditions fluctuating at a rate and level greater than traditional HVAC equipment is capable of handling (Figure 1). Precise equipment and sophisticated control are required to maintain ideal growing conditions.

Plants are sensitive to bacteria, viruses and molds such as powdery mildew and bud rot. The introduction of these harmful contaminants can have disastrous results on the crop. By providing up to 100% recirculation and no outside air, the GRW unit protects the crops from airborne pollutants.

Unlike comfort conditioning applications, the load associated with an indoor horticultural environment does not change with outdoor conditions. The HVAC equipment must be able to provide precise control 365 days per year, even as temperatures outside turn cold and the airstream inside remains humid. Equipment failure can result in catastrophic degradation of operational capacity and potential crop loss. The GRW design elements provide the solution by continuing operation at reduced but managed capacity even in the event of a part failure, providing exacting performance and failure protection.

Energy efficiency has a far greater impact on operating cost in a horticultural system than in most other applications. With continuous operation, the energy consumption for environmental control can be 25% of revenue for an indoor horticulture operation. Electrical power for HVAC is one of the largest operating costs in a modern facility. The peak operating loads occur for several hours per day, every day, whereas typical comfort cooling may operate under peak conditions only for several hours or days throughout the entire year.

Figure 2: Dehumidification Energy Cost

For example, in a greenhouse being maintained at 75 °F (24 °C) at 50% relative humidity, the GRW is capable of supplying over 200% of the dehumidification capacity per cooling ton when compared to a typical comfort cooler operating at standard conditions of 400 cfm/ton (Figure 2).

Assuming a system had an Energy Efficiency Ratio of 10, and electricity costs of $0.10/kWh, the annual costs of dehumidifying 125 gallons (473 L) per day – the approximate requirements of 1,000 plants at 16 oz (473 mL) per day – would be over $24,000 for standard air conditioning, as shown in Figure 2. The Price GRW dehumidification energy demand would be $11,500, providing cost savings of up to $12,500 annually.

Price utilized CFD analysis and rigorous testing in ambient conditions as low as -40°F to create the low leakage, energy efficient cabinet design that protects against internal condensation and energy loss.

The Price GRW has been tested in our world class Psychrometric Chamber Laboratory and Environmental Chamber to meet AHRI 440, ASHRAE 84, CSA C439, ISO 16494, and AHRI 1060 standards.

The Price GRW is purpose built for your application. To learn more about the GRW, or to schedule a visit, please contact your local Price Representative, or visit

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