As the demand for energy-efficient and sustainable HVAC solutions grows, integrating heat pump technology into rooftop units (RTUs) has become a compelling option for commercial and industrial applications. Heat pumps have been around for over a century, but recent compressor technology and system design advancements have significantly improved their efficiency and applicability in various climates. This article explores the integration of heat pump technology into RTUs, addressing key considerations, limitations, and strategies for optimizing performance.
The Traditional RTU Replacement Approach
Traditionally, RTU replacements follow a like-for-like approach, typically consisting of direct expansion (DX) cooling and gas heating. This method is simple and cost-effective, requiring minimal electrical and gas infrastructure changes. However, as building owners and facility managers seek to reduce carbon footprints and operational costs, transitioning to heat pump technology offers an appealing alternative.
Understanding Heat Pump Technology
Heat pumps work by utilizing refrigeration cycles to generate useful heat. Instead of burning fossil fuels, they transfer heat from the outside air to the inside space, making them an energy-efficient heating solution. The key benefits of heat pumps in RTUs include:
Integration of Heat Pumps into RTUs
Modern heat pumps can be seamlessly integrated into packaged RTUs, but several factors must be considered:
Cost Considerations: Are Heat Pumps Expensive?
With any major building asset, the total cost of ownership, including initial cap-ex costs and ongoing op-ex costs, should be considered.
From a cap-ex standpoint, heat pumps are still more expensive than traditional heating sources like natural gas. However, traditional rooftop units with DX cooling already include the vast majority of components needed for heat pump heating. Only a few additional components are required to transform a DX-cooling system in an RTU into one that can also provide heating.
Because of this, a rooftop unit with heat pump heating could be as little as 10% more expensive than a comparable cooling-only model.
From an op-ex standpoint, natural gas utility costs in the Southern Ontario region are cheap relative to the cost of electricity on a kWh-to-kWh basis. In the past, it has taken an extremely efficient heat pump with a very high annualized COP to “beat” the cost of natural gas.
However, in recent years, regulatory forces and incentives are slowly bridging the gap between the cost of electricity and the cost of natural gas. These forces are making it increasingly more economically attractive to heat with heat pump heating over natural gas for longer periods of the heating season.
Backup Heating Strategies
To ensure reliable performance, backup heating solutions are essential. There are two important distinctions to understand when considering backup heating:
A rooftop unit equipped with supplemental heating will be able to provide useful heat pump heating for significantly more hours of the heating season than a unit equipped with emergency backup heating will. For units equipped with natural gas backup heating, this means a further reduction in carbon emissions and more flexibility in deciding when to use heat pump heating and when to use gas.
Electric resistance heating, while effective, comes with high electrical demands and retrofitting challenges. More advanced rooftop units offer flexibility to help reduce the overall electrical nameplate rating, including:
Avoid Installing More Than Needed
Oversizing a heat pump to maximize heating performance on a winter day can cost energy efficiency and stability, especially during milder ambient conditions, when we spend the majority of our heating hours.
When sizing your heat pump, consider more than design-day performance. Consider the ambient temperature ranges in which we spend most of the heating season and strike a balance between heat pump capacity and expected annualized runtime.
Look for other ways to reduce heating load, including:
Conclusion
Integrating heat pump technology into RTUs is a forward-thinking approach to HVAC system design. By understanding the benefits, limitations, and key considerations such as backup heating, defrost cycles, and energy recovery, building owners and facility managers can make informed decisions that enhance energy efficiency, reduce operational costs, and support sustainability goals.
Heat pump technology has come a long way, and with the right strategies in place, its integration into RTUs can be a game-changer for the HVAC industry.