When I tell people that we just throw our vegetables into our walk-in cooler at any time of the year, they either get excited and ask more questions or put up a wall and start coming up with excuses about why they could never afford to have a walk-in cooler. This post is for both types of people, because we're going to look at some numbers to examine the true costs of cooling our food with a typical refrigerator as compared to a walk-in cooler.
If you are just joining us, the video below will show you the three different methods we have used to cool our walk-in cooler at all times of the year and this earlier post has some nice diagrams to explain these different cooling methods.
The cooling method I am most excited about right now is the use of an air-to-water heat pump, which can extract heat from the cold room and use it to heat our hot water tank. In theory, this multi-purpose use of the air-to-water heat pump should lower our combined costs for keeping our cold room cold and also keeping our hot water hot, but we're taking some time today to see how the numbers actually look.
The main cost comparison I want to make is between a typical household refrigerator and our walk-in cooler which is now cooled with a heat pump, and in order to share a fair comparison I have been conducting a lot of power measurements! The result of all these power measurements and a lot of math is the summary sheet shown below.
Read on for a breakdown of the key numbers.
Initial Costs
The first thing I noticed when looking into refrigerator pricing is that there is a huge variance. I could find a very basic refrigerator for $1000 or spend up to $10,000 if I wanted. I opted to use a pretty conservative price of $2000 for an average new refrigerator.
The initial costs of our walk-in cooler and heat pump are comprised of the $4444 we paid for the Sanden CO2 heat pump and an additional $2000 for building materials to construct an insulated room to use for the walk-in cooler.
Operating Costs
The annual operating costs depend on the power consumption of each device and the price of electricity. The price of electricity was easy to determine because we pay a fixed rate of $0.1638 per kWh. The power consumption estimates were a bit trickier.
We don't have a regular refrigerator from which to take power measurements right now but online estimates suggested daily power consumption anywhere between 2 kWh and 5 kWh. I decided to use the best case scenario of 2 kWh/day for our refrigerator cost calculations, but your costs could be significantly more if you have a more power hungry refrigerator. With the power consumption of 2kWh/day and an electricity cost of $0.1638/kWh we can calculate an annual refrigeration cost of $118.
The cooling cost for our walk-in cooler was easier to measure but it's less consistent because of the different cooling methods we employ in the winter and summer. In the winter, when the air is well below freezing outdoors, we can just blow that cold air into our cooler with a couple of small vent fans and effectively regulate the temperature without any fancy heat pump technology. However, not everyone has an abundance of cold air to draw upon for half of the year, so for the purpose of this cost comparison, I imagined using our heat pump to cool our walk-in cooler for all 12 months of the year. Then, I used an Efergy power meter to track the power usage of this heat pump for a week in July and again for a week in September. The July average was 8.95 kWh/day and the September average was 8.07 kWh/day. I would attribute the lower power use in September to the lower soil temperature around the outside of the cold room in September. No estimate I make is going to match your climate or walk-in cooler conditions exactly, so for the purpose of this const comparison I just used an average of 8.5 kWh/day for our heat pump power consumption
So if a refrigerator uses 2kWh/day and our heat pump uses 8.5kWh/day, why is the operating cost for the walk-in cooler listed as a cost savings of $277/year? That's all thanks to the multipurpose value of the heat pump. The 8.5kWh/day that we put into our heat pump serves to cool our walk-in cooler AND heat our family's hot water tank. Without our heat pump serving these purposes, we would be drawing 2kWh/day to power a refrigerator and another 11.2kWh/day to heat our hot water tank, (Yes, I measured this too.) for a total of 13.2kWh/day. So by using the heat pump for these two purposes, we save 13.3kWh - 8.5kWh = 4.8kWh of electricity every day for a cost savings of $0.79/day and $277/year.
Cumulative Cost/Savings
This was the most interesting section to me, because I new the heat pump and cold room construction costed more initially and I knew the heat pump could save us some money thanks to its water heating ability, but I still didn't know how long it would take to payback that initial investment...if it even could. The yearly cumulative cost comparison shows us that the payback potential for the walk-in cooler is very real! After 12 years, the cost of the walk-in cooler becomes lower than the cost of the refrigerator, and after 25 years when a refrigerator has cost its owner almost $5000, the walk-in cooler investment has more than paid for itself in energy savings. Therefore, this cost comparison backs up my initial claim in the title of this post by showing how we actually did upgrade to a walk-in cooler for FREE. Initially, I had hoped that one could upgrade to a walk-in cooler for the equivalent cost of a refrigerator (ie. FREE) and the data shows us that we can make up the cost difference in just 12 years. That's exciting, but since the heat pump and cold room eventually recuperate ALL of their costs, the title of the post could read "How to Build and Operate a Walk-in Cooler for FREE"!
That's where we'll leave this subject for now, but I know there are a few finer details I have skipped over for the sake of simplicity and clarity. It was a challenge to present this subject in a way that wasn't terribly discombobulating. I plan to add a few more bits and pieces to this post in the near future, so if there is something specific you're wondering about, use the contact form below to send me your question. The answer might be something I can add to this post.
