Longo’s Newest CO2 Refrigeration System One For The Record Books
About a month ago, Longo Brothers Fruit Markets opened a new retail location in Stouffville, Ont., that achieves a near-net-zero rate of electrical energy consumption. The project is the ﬁrst of its kind for a supermarket in Ontario, and is projected to save 52 per cent in average energy consumption, while improving air quality and maintenance management.
A number of different systems contribute to meeting that energy-use goal, from solar panels and the latest building envelope technologies, to the refrigeration, mechanical and HVAC elements of the design, but a cornerstone of the project is the combined cooling, heat and power (CHP) system.
It uses natural gas from the grid to provide 150 kW of electricity and approximately 700,000 BTUs of heat reclaim. This reclaimed heat can be used in a variety of ways, including driving an absorption chiller that in turn pre-cools the top side of a carbon dioxide-based refrigeration system.
This allows for the CO2 system to operate in a sub-critical mode as opposed to transcritical, resulting in higher operating efﬁciencies and a lower energy consumption.
The Journey To C02
Neelands Group Limited has long partnered with Longo’s in the design and installation of the supermarket chain’s refrigeration and HVAC systems.
”We started using glycol for refrigeration in 2006 as a secondary cooling medium to reduce the HFC refrigerant use,” says Tom Quaglia, senior construction manager at Neelands. ”When we brought the design to Longo’s, the decision was made to use the propylene glycol for medium temperature and keep using HFC for low temperature applications.”
At the time, North American manufacturers were doing different things with CO2 and dabbling with it to reduce HFC usage, he adds.
”Nothing had come out as mainstream. Glycol did, but we knew what we did in 2006 was not the end game.”
Around 2009, as CO2 gained traction in Europe, and the technology started making its way to North America, a manufacturer presented the concept of using CO2 transcritical refrigeration to Neelands. Quaglia says the time was right to look into it further as a viable refrigeration evolution.
Progressing To Zero
The inspiration for Stouffville came three years ago when representatives from Longo’s, Neelands and S2e, a developer of sustainable energy solutions, toured a site in California that used a combined heat and power unit and an absorption chiller.
”Between us, we came back to Longo’s with a plan to build a near net-zero store that combined the heat recovery with CO2 refrigeration,” Quaglia says.
In their design, the electrical energy produced by the CHP is recovered and used to ﬁnish condensing the CO2 refrigerant during the summer months.
”On the hottest days of the year, we have to use compressors to ﬁnish condensing the refrigerant,” Quaglia notes. “CO2 tends to be inefﬁcient when we need to use the compressors. If we can eliminate that, we can have an efﬁcient system 12 months of the year.”
The heat from the CHP unit drives an absorption chiller to deliver chilled water to the refrigeration system.
”That’s a very unique approach for any supermarket in Ontario,” he explains. “You see CHP units used a lot in agriculture if they have greenhouses, but not in supermarkets”
The energy generated by the CHP is also used to heat the building throughout the year, Topan adds. ”Supermarkets are unique in that you have to pump heat into them all the time. In the summer you are always having to dehumidify the environment. When you do that you have to reheat the air to a comfortable temperature.”
The next push for Longo’s, S2e and Neelands is moving from near net-zero to a net-zero model, Quaglia notes. ”We’re not at that point quite yet, but we’re working on it.”
A Milestone Moment
In 2012 Neelands decided to try out a CO2 and glycol design in a Longo’s store in Oakville, Ont., making it the first CO2 transcritical system in Ontario (others had previously been done in B.C. and Quebec).
They continued to use the same refrigeration design in two additional stores, using CO2 refrigerant for low temperature and glycol for medium-temperature applications. The next store, located at Applewood Mall in Etobicoke, Ont., was the first time they were able to explore a 100 per cent transcritical CO2 model. ”We haven’t looked back since,” says Chris Topan, Neelands’ supermarket technical solutions representative.
Because the concept was relatively new, capital costs were higher, but Topan says that equipment prices have since come down with CO2 becoming more mainstream.
”The parts are not as specialized as they once were and manufacturers are producing more systems. The investment in technology delivers payback much sooner.”
Another big saving is the cost of refrigerant itself. ”HFC chemicals are expensive. But CO2 is a natural refrigerant that’s quite cheap.”
As for the refrigerated display cases themselves, the differences aren’t significant. ”CO2 does require a special coil and the expansion valve is electronic rather than mechanical. Otherwise they are pretty much the same,” Topan explains.
A Lesson In Servicing C02
Servicing a transcritical CO2 refrigeration system has its own unique challenges. When Neelands piloted its ﬁrst installation, part of the job was getting the service technicians comfortable with servicing on a regular basis, Quaglia says.
The main challenge is that pressures are much higher than with HFCs, he says. ”On the high side it could be 1,740 psi during the hottest days in summer.
”HFCs operate in the 300 range. Because there is quite a difference in pressures, there is also a difference in the materials needed to maintain the pressure differential. It took a bit of getting used to.”
Another difference of note is the condensing process. HFC refrigerant condenses to a liquid at an outside temperature of 80°F (27°C).
”CO2 does not fully condense to a liquid. It’s a combination of vapour and liquid that comes back to the expansion valve and then condenses to a liquid,” Quaglia explains.
He adds that while there is little difference on a cool day, summer days are different. ”With an HFC system, the rooftop system does the condensing. With a CO2 refrigeration system, a gas cooler can sometimes condense it, but not always. Otherwise you need to use the ﬂash tank inside the mechanical room.”
Finding leaks can also be challenging. ”Typically, there is 400 parts per million of CO2 in the air we breathe, so you need a good quality leak detector,” Topan advises.