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Rooftop HVAC systems

There are some definite advantages to rooftop Heating Ventilation Air-conditioning Cooling (HVAC) systems: they are smaller, easy to install, affordable and can scale to meet changing requirements. Recent advances in HVAC technology are making these systems even more attractive, however, with increased efficiency and improved controls doing away with traditional trade-offs.

Neil Cameron, area general manager, Johnson Controls Building Efficiency Africa.

These are important considerations for this user market, namely small and medium sized buildings (up to 10 000 m²) such as office parks and shopping malls, as it addresses pressing business imperatives such as better management of energy consumption and cost control.

In the past, low cost has often been synonymous with low sophistication when it comes to rooftop HVAC solutions. With fixed-speed air distribution, manual on/off controls, basic components and no built-in intelligence, these systems were neither energy efficient nor easy to control. These compromises are fast becoming a non-issue. Today, these same systems are now compatible with any building management system (BMS), which means they are informed by sensors and intelligent management features, are configurable and can adapt their outputs to the weather and the environments they serve.

Variable speed drives (VSD) built into motors enable effective capacity variation, increasing supply fan performance and facilitating changing of air volumes to meet the needs of the facility. Return fans make use of energy from exhaust air to heat fresh air, lowering energy consumption (by recirculating air the requirement for conditioning air is lowered), while CO₂ sensors and variable air volume (VAV) diffusers placed within ducts work together to ensure indoor air quality and temperature requirements are optimised for each specific space.

These rooftop solutions come in standard packages and different capacities (from 17 kW to 84 kW) with different options. There are cooling only, as well as heating and cooling models. Economising dampers, VSDs, return fans, CO₂ sensors, thermostats, smoke detectors, electric heaters and filter kits for heat recovery.

These solutions are literally plug-and-play and are eco-friendly, making use of environmentally friendly R410A refrigerant. They are also highly efficient, with a coefficient of performance (COP) of almost 4, a big improvement on the previous COP of 2.5 that these systems delivered. (COP is the ratio of heating or cooling provided to electrical energy consumed.)

With a fairly good lifecycle – certainly one that will outlive a standard facility lease agreement – these systems offer great value. They are changing how rooftop units are perceived, offering an improved return on investment with lower running costs and optimised energy consumption.

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