Decarbonizing Space Heating with Refrigeration Heat Reclaim

In our recent article, Decarbonization 101: Key Decarbonization Strategies for Retailers, we covered several decarbonization strategies that can be implemented by facilities leaders as part of their journey toward achieving net zero emissions. Now, we’re taking this opportunity to deep dive into one particular decarbonization strategy for food retail and other businesses that use refrigeration equipment — refrigeration heat reclaim.

Decarbonization Meaning

“Decarbonization” simply means reducing the amount of carbon dioxide (CO2) and other greenhouse gases released today into the Earth’s atmosphere by both natural and human activities. These gases trap heat and warm the planet, making decarbonization vital for combating climate change.

Decarbonization entails everything from finding cleaner and more environmentally friendly ways of generating energy, such as using renewable sources like wind and solar power instead of burning fossil fuels like coal and oil, to increasing energy efficiency and decreasing the pollution emitted by automobiles, trucks, and factories.

By adopting a comprehensive decarbonization strategy, supermarkets and other food retailers can dramatically reduce their carbon footprint while also achieving significant long-term financial benefits. While the word “decarbonization” can include any measure taken to minimize any greenhouse gas emission from any source in any way, it is most often commonly applied to eliminating GHG emissions associated with the combustion of fossil and other carbon-based for heating, cooking, and other purposes.

Fossil Fuel Combustion Contributions to GHG Emissions

One of the most essential decarbonization strategies is displacing natural gas, propane, oil, and other carbon-based fuels commonly used for heating and other purposes.

In terms of global warming impact, a very significant percentage — 70% — of total CO2 emissions result from the use of carbon-based fuels (mainly fossil fuels but today also including plant-based fuels like ethanol, wood pellets, peat, and others) for building space heating, electricity generation, steel production, cooking, and other purposes.

Considering the substantial contribution to overall greenhouse gas emissions of carbon-based fuel use, phasing out the use of natural gas, propane, and other combustible fuels is essential to get to net zero and stop or even moderate climate change.

Decarbonizing Space Heating in Supermarket Facilities

One of the biggest questions on the minds of grocery facilities leaders is how to displace the use of natural gas, propane, and other fuels used for heating of all kinds in their stores. After all, natural gas usage is typically on the order of 50K–100K CCFs per year for the average supermarket, depending on geographic location. This amounts to 1,000,000 to 2,000,000 kWh of additional electricity usage per year if store heating requirements are met with electric heat.

“While most conversations about decarbonization are focused on electricity use and greener sources of electricity, for commercial facilities there’s a very large amount of energy use on the heating side,” says Tom Mathews, a mechanical engineer and industry expert with nearly four decades of experience in the food retailing and distribution industries. “For one grocery chain, 35 to 40% of their GHG emissions come from heating fuel use alone.”

For most retail food stores and for commercial buildings in general, space heating is commonly done in two ways. The first is by gas furnaces, which burn either natural gas or propane and transfer the heat generated to air that is continuously circulating by supply air throughout the building. The second method of heating is by using a gas or propane-fired boiler to heat water, and then pumping the hot water to areas of the building that require heat.

Similarly, domestic hot water — that is, water used for washing and sanitizing food preparation areas, hand washing, and other similar uses — is produced by burning natural gas or propane in a variety of hot water heating equipment types.

In buildings such as grocery stores, refrigerated distribution centers, convenience stores, food processing plants — any facility with substantial need for and use of refrigeration systems — heat is being generated all the time. This is where refrigeration heat reclaim comes in …

The Rise of Refrigeration Heat Reclaim

For any facility with refrigeration, the use of refrigeration heat reclaim is one particularly effective strategy for reducing the burning of fossil fuels.

“Refrigeration heat reclaim” means recovering the heat refrigeration systems take from refrigerated cases and coolers and using it for store space and hot water heating.

Typically, this refrigeration heat is just “rejected” to the outdoor ambient via refrigeration condensers, those units one sees on building roofs with banks of fans pulling the heat from the circulating refrigerant and pushing it into the outdoor air. But when space heating or hot water is needed, this waste heat can be redirected to these uses, instead of being “thrown out,” Tom explains.

This approach is especially important in supermarkets because space heating is needed both in the winter to keep the store comfortable and year-round to keep store humidity levels low even when it is humid outdoors. Controlling store humidity levels keeps the store more comfortable and reduces store refrigeration system energy usage.

Additionally, refrigeration heat reclaim can eliminate fuel combustion altogether, resulting in very major reductions in GHG emissions and operating expenses, and substantial progress toward achieving net-zero emissions.

“We are not talking about some new concept,” Tom says. “Refrigeration heat reclaim is an energy efficiency and sustainability measure that goes back decades. However, due to moderating natural gas prices and refrigerant leakage concerns, its use leveled off over the last 20 years.”

Even where refrigeration reclaim has been done, it has almost always been partial heat recovery, with systems designed to capture 30% to 50% of the available heat. But now, with building operators being forced by climate change to find ways other than burning carbon-based fuels to heat their facilities, 100% of refrigeration “waste” heat reclaim is being embraced, allowing supermarkets in particular to eliminate 100% of their use of natural gas, propane, and other carbon-based heating fuels.

This is what’s new, Tom explains – getting all of the available heat, not just some of it, and using this to displace all current gas usage for space and hot water heating. At the same time, ways are being developed to move to 100% refrigeration heat reclaim without increasing refrigeration charge, leaks, and resulting refrigerant-related GHG emissions.

“Heat reclaim is going to be one of the centerpieces of greenhouse gas emissions reduction at most supermarkets,” predicts Tom.

Heat reclaim is going to be one of the centerpieces of greenhouse gas emissions reduction at most supermarkets.Tom Mathews, SVP of Sustainability at CBES

“Refrigeration equipment in a supermarket is like the world’s biggest heat pump,” Tom goes on to say. “There is a constant supply of heat coming from it. This heat can be used to heat sales areas and other spaces during cooler parts of the year instead of burning gas or propane or running electric heat.”

He adds, “Now it’s no longer waste heat but a valuable source of heat with the capability of displacing the entirety of the 50K CCF of gas previously used by a store — not to mention, all of the carbon emissions associated with that.”

If more heat is needed, the refrigeration system discharge pressures can be raised to get more and higher temperature heat from the system. Refrigeration system energy usage does increase during periods of elevated condensing pressure operation, but normally this is still less costly than using direct resistance electric heat or owning and maintaining backup natural gas furnaces. For most supermarkets south of the 49^th parallel (our border with Canada), refrigeration heat reclaim can on its own meet 100% of store space and water heating requirements.

In this way, decarbonizing space heating with refrigeration heat reclaim is an exciting step forward for the environment as well as a highly effective way for facilities to save money. No wonder why it’s making a comeback. In terms of ROI, Tom says, this decarbonization strategy is one of the highest payback measures available in terms of dollars per ton of CO2 spent.

Refrigeration Heat Reclaim Modifications

The modifications required for enabling 100% refrigeration heat reclaim are relatively modest, especially considering the substantial reductions achieved in GHG emissions. Here are two of the most popular technologies that underpin 100% heat reclaim measures:

1. Direct Refrigerant-Based Heat Reclamation

With direct heat reclaim, hot refrigerant discharge gases are circulated directly to an air handler or rooftop unit — either an existing piece of equipment or new system — that has special heat reclaim coils in them. Instead of extracting just 30% of the heat (the available “superheat”), 100% of the heat is extracted by allowing or forcing “full condensing” of the refrigerant to occur.

“The coils are bigger and designed in a different way to fully condense the refrigerant,” Tom explains. “This allows the system to provide enough heat to completely, or almost completely, displace the natural gas, propane, or other heating fuels previously in use.”

Formerly, when refrigerant discharge gases were circulated to the heat reclaim coil, the gases gave up part of their heat (were “desuperheated”) but stayed in the gaseous state. However, to maximize heat reclamation, the hot discharge gases must be fully converted back to liquid refrigerant, that is, fully condensed. This allows the “latent heat” to also be captured.

Tom explains, “With this method, you don’t just cool the gases but instead condense them all the way to liquid. This is what allows you to get 100% of the available heat.”

2. Indirect Heat Reclaim

Direct heat reclaim as described in (1) above can require an increase in refrigerant charge, which can sometimes mean higher refrigerant losses from the system and therefore an increase in GHG emissions.

According to Tom, facilities have an effective way to avoid this issue. Instead of directing hot refrigeration system discharge gasses directly to the heating coil within the rooftop unit or air handler unit, they can install a water-cooled heat reclaim condenser at the refrigeration rack or condensing unit and then circulate the heated water to a water coil in the rooftop unit or air handler unit.

With indirect heat reclaim, there is some loss in efficiency and this approach should be required only where store refrigeration systems are chronic leakers and there’s little chance of fully eliminating refrigerant leaks on a permanent basis.

3. Indirect Heat Reclaim with Single Water-Cooled Condenser

A third approach is as described in (2) above except a single water-cooled condenser is installed rather than adding a heat reclaim-only water-cooled condenser and leaving the existing air-cooled rooftop condenser in place.

With this third system, hot condenser water is directed either to the heat reclaim coil or to a new fluid cooler installed in place of the air-cooled rooftop condenser. Again, there is some loss in system efficiency, but as Tom says, “You have a much smaller refrigerant charge, much smaller even than before 100% heat reclaim was added.”

The net balance might be expressed as Net Benefit =(reduction in GHG emissions from displaced natural gas/propane/fossil fuel GHG emissions) + (addition in GHG emissions from additional electricity usage for extreme cold weather high pressure refrigeration system operation) + (addition in GHG emissions from any increase in refrigerant losses) + (reduction or increase in greenhouse gas emissions due to increased or reduced condenser fan/fluid cooler fan electrical energy usage)

Choosing a building’s refrigeration heat reclaim modification depends on factors like the store type, location, your specific refrigeration system, and your specific HVAC system. To make the right decision for your facilities, consult with an experienced engineering partner who can assess your situation and recommend the most suitable approach.

The Impact of Refrigeration Heat Reclaim

With decarbonizing space heating by heat reclaim, grocery stores and other commercial facilities can reduce GHG emissions by 30 to 40% while significantly reducing operating expenses while they’re at it.

Similar to reducing refrigerant leakage, refrigeration heat reclaim directly reduces GHG emissions. This direct connection to emissions reduction enhances the likelihood of widespread adoption and offers more immediate environmental benefits compared to other sustainability measures like adopting solar or wind power, whose effects are typically realized further upstream at the power generation plant.

The cost of retrofitting existing store HVAC and refrigeration systems to utilize refrigeration heat reclaim for all store space-heating needs will vary depending on the type of existing HVAC and refrigeration system and equipment, but $ 85,000 to $135,000 is a reasonable starting range.

Savings will include avoided gas or propane purchases and avoided electricity use. (Remember, when these improved heat reclaim systems are operating, the refrigeration condenser fans are not needed and shut off.) Estimated total annual savings depend on local gas and electric rates and annual space heating and dehumidification reheat requirements but should be somewhere between $30,000 and $60,000 per year. Utility rebates are now becoming available for these conversions, often called “beneficial electrification” in the electric utilities’ vernacular.

Decarbonization Solutions for the Future of Retail

By utilizing refrigeration waste heat, food retail facilities can eliminate the combustion of fuels such as natural gas and propane for space heating and hot water production, dramatically reducing greenhouse gas emissions and decreasing energy consumption. The result is a positive impact on the planet as well as the pocketbook.

CBES is dedicated to helping our customers reduce their emissions and energy costs with a customized decarbonization strategy. Reach out to our team to learn more about our end-to-end engineering, programming, and sustainability solutions.