Industrial heat pumps are refrigeration subsystems that use waste heat from the refrigeration system to heat water or glycol. Normally, the heat that is removed from the building in the ammonia (NH3) evaporators is rejected to the atmosphere through evaporative condensers. Not only is the heat wasted, but the owner pays for powering the condenser fans, water evaporated, and chemical dosing.
This blog explains how a heat pump works, the advantages of using one in your refrigeration system, and considerations to determine if a heat pump is right for you.
How Does a Refrigeration Heat Pump Work?
In a central refrigeration system, a heat pump is typically connected in parallel to the condensers. It includes an ammonia compressor that boosts the system head pressure to allow for much higher condensing temperatures that make heat recovery possible. The higher pressure, hotter discharge vapor rejects heat to water or glycol in the heat pump condenser. The condensed NH3 liquid then returns to the refrigeration system, and the hot water/glycol is pumped out to the plant to supplement hot water or utility heating loop demand.
The Advantages of Industrial Heat Pumps
- Decarbonization: Heat pumps use “free heat” from the refrigeration system and are fully electric. The boiler load can be reduced by the heat pump capacity, lowering the plant’s natural gas consumption, utility cost, and scope 1 (onsite) emissions.
- Hot Water/Glycol Capacity: Heat pumps generate hot water/glycol. If a plant needs additional hot water capacity (e.g., plant expansion, aging boilers, etc.) a heat pump can be a good alternative to installing more boiler capacity.
- Refrigeration Condensing Capacity: The heat exchanger in the heat pump acts as an additional NH3 condenser. If a refrigeration system needs additional condensing capacity (e.g., if a condenser needs to be retired or due to a refrigeration system expansion), a heat pump can be a good option. Just keep in mind that the heat pump needs an active heat sink (hot water/glycol user) to reject heat from the refrigeration system.
Is a Heat Pump Right for Your Facility?
Remember, heat pumps move heat, they don’t generate it. A good heat pump application has a heat source (refrigeration load) that occurs simultaneously with a heat sink (hot glycol/water user). A heat source is any refrigeration load like chillers, freezers, or HVAC. Heat sinks are any hot water or glycol user such as product heating, sanitation hot water generation, or heating hydronic loop water. The loads must occur simultaneously for the system to make a good heat pump application.
To determine if your refrigeration system will generate enough heat to supply a heat pump, create a load profile of refrigeration load plotted over heating load versus time (see graph below). Any time the refrigeration load (heat source) is greater than the heating load (heat sink) a heat pump can provide the full heating capacity. In this example, from 5 am to 10 pm the refrigeration load is greater than the desired heating load, so a heat pump can provide the full heating load at this time. From 11 pm through 4 am, the heating load is greater than the refrigeration load, so a heat pump cannot provide the full heating load during this window, and supplemental heating or hot water storage is needed.
Other factors to consider:
- Heat pumps generate 140-200°F hot water or glycol. The heat load must be satisfied by fluid in this temperature range.
- Heat pumps can be engineered for a wide range of capacities, but typically 2–15 MMBtu/hr (2,000,000–15,000,000 Btu/hr). Larger heating needs may call for multiple heat pumps or supplemental heat sources.
- Heat pumps can be large skids, there needs to be adequate space available in or near the refrigeration engine room.
- Heat pumps require additional electrical infrastructure and should be planned for in advance.
Conclusion
If your facility checks all the boxes above, an industrial refrigeration heat pump might be a good fit for your system. Industrial heat pumps provide a proven solution for facilities looking to improve their energy efficiency and reduce their carbon footprint through heat recovery and electrification. Embracing this technology can lead to a more sustainable and economically viable future for industrial operations.
