April 2012 by Plumbing and HVAC

■ Refrigeration Fig. 1: This table compares vapour compression with natural gas fired absorption, using utility costs and CO2 data from Saskatchewan.

Alternate heat refrigeration strategies Continued from page 25 increases the net refrigerating effect of a system and thereby decreases the power requirements of the compressors. A grocery store in New York State has installed a CHP system such as this with an estimated payback of under 10 years. In England, results as high as 20 percent reductions in primary energy consumption have been published.

countries that have a significant number of cooling days. At least one manufacturer is building adsorption chillers almost exclusively for this application. In a number of jurisdictions there are grants and energy rebates for operating combined heat and power systems (CHP). These systems use a natural gas or diesel engine to generate both power and heat. Alternate paths The theory is that the costs associated with the There are many different ways that these heat distribution losses in the power grid are negated by powered refrigeration technologies can be generating power on site and recovering the heat. implemented. Now that we’ve discussed using heat We are not going to go through the merits of the to power an absorption (or adsorption) cycle to CHP systems here, except to note subcool liquid in a CHP application, they are often of limited use in what’s stopping us from moving forward applications that do not require the and using the chilled water generated in a heat. To take advantage of this heat, a solar refrigeration system to do the same? number of supermarkets are piloting Consider an outdoor air cooled tri-generation systems. This means refrigeration system. In most places in that a CHP system is running Canada they are designed to operate in at (typically on natural gas) and least a 95°F ambient. This results in a generating power, hot water, and cold These solar collectors design condensing temperature of 110°F water. The cold water is generated by are used for a solar or higher. using a portion of the heat to power adsorption plant inOne of the problems I deal with an absorption chiller. frequently is the imbalance of condensing stallation in Japan. One of the most common ways to (Mayekawa photo) unit capacity and evaporator capacity for utilize the resulting cold water is to use outdoor condensing units that serve a it to subcool the liquid refrigerant in the main small number of loads. The condensing unit must refrigeration plant. Subcooling liquid refrigerant be sized to provide the design load on the hottest day,

but it almost never runs at those conditions. Consequently, the unit can be grossly oversized for winter operations. If we were able to implement a solar refrigeration system to provide subcooling on the very hot days, we might be able to get a much better load balance and decrease the size of our equipment. There are more heat recovery and energy savings applications for heat generated refrigerating systems than could possibly be mentioned here. Are we at a point where a contractor can order anything they can dream up and install it next week? We’re not. Right now there are not a lot of options for mass produced components and systems, particularly for small applications, but that will change. When it does, I think it would be prudent for all of us to brush of on our adsorption and absorption refrigeration skills. We are going to need them. ✚

Greg Scrivener is project and design manager for a Polar Refrigeration Service Ltd. in Saskatoon. He is a journeyman refrigeration mechanic, a licensed gas fitter, holds RSES CMS designation in commercial refrigeration and is a mechanical engineer in training. He can be reached at gscrivener@polarservices.ca.

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