CCAT Cold Box Interview with Sean Armstrong 02/26/2009
Jessica: What is the average temperature a standard refrigerator keeps fresh produce around?
Sean: I don’t know about produce, but the general standard for a refrigerator is 35-38 degrees F. The purpose of cold temperatures is to slow bacteria growth, so it’s not an absolute requirement—higher temperatures mean the food spoils sooner.
Jessica: What is the average internal temperature of a cold box in Arcata?
Sean: In the winter it’s about 45 degrees. In the summer it’s about 55 degrees.
Jessica: Does internal cold box temperature fluctuate between night and day hours?
Sean: Yes, and that’s the goal of thermal mass. More granite, more liquids, etc. mean that the cold night temperature persists through the day.
Jessica: Is wood as a main building material best for this type of structure? Redwood? Other local woods? Metal?
Sean: Metals is the best exterior material, and stone is the best shelving. Stone thermal mass on the side walls also helps.
Jessica: Is odor reduced by the passive cooling and ventilation, if not eliminated?
Sean: I don’t understand what you mean by “odor.” The food just smells vaguely like food.
Jessica: How does a cold box differ from a standard refrigerator in regards to lifespan and longevity of produce? Is shelf life reduced/ extended?
Sean: We keep all food, meat, dairy, condiments, and produce in the fridge. I would guess that the shelf life is reduced a few days, depending on how sensitive each food is. In the winter we keep meat in the cool closet safely for about three days. Milk is safe for at least a week, and vegetables are also safe for about the same amount of time as in a fridge, especially because they don’t get dehydrated by the low humidity of a fridge.
Jessica: What else can be stored safely within a cold box besides fresh fruit and vegetables?
Sean: Everything. You just eat it a little sooner, like you would if you were car camping and your food was in a cooler instead of a fridge.
Jessica: Are cold box’s effective in both winter and summer (specific to Arcata)?
Sean: Definitely in the winter, but summer time it’s not very effective as currently designed. The outdoor temperatures are too high, even at night, to safely store food for long periods of time. The solution will be to simply store food for less time and eat it before it spoils.
Jessica: Beside insulation in the form of panels, are there other materials that have the same properties?
Sean: Yes, reflective bubble wrap can work although it has less R-value. The real goal is thermal mass though—holding the cold is more important than resisting heat infiltration.
Jessica: Does spacing between the shelves and spacing within the slats of a single shelf need to have specific dimensions?
Sean: No, just try to make it like a “normal” fridge with dividers and sufficient space. Fridges are well designed for use, so follow that model.
Jessica: What is the average amount of energy saved by using a cold box instead of a standard refrigerator?
Sean: The numbers are extremely variable depending on the size and efficiency of the refrigerator. We saved about 600 kWh per year by unplugging the fridge, or about $84.
Jessica: Average cost to build a cold box that will be appropriate cabinet size for the CCAT kitchen?
Sean: Hm. Don’t know.
Jessica: Do you recommended any type of fastener to hang box on wall that will withstand the load?
Sean: Sorry, don’t know.
Jessica: Do you recommend any design or material elements to help make this a rockin’ cold box?
Sean: Metal exterior with slabs of thermal mass lining the walls. Shelves made of granite or marble with small ventilation holes drilled in them.
