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I recently received a question that went like this:  “What does it mean to be a one ton air conditioner?”  The short answer is that it can move 12,000 Btu’s (British Thermal Units) per hour.  This got me thinking about why we refer to refrigeration amounts in tons rather than just the more descriptive energy transfer rate (Btu/hr).  Turns out, there is a neat and practical reason why air conditioning and refrigeration systems are measured in tons.

Before mechanical refrigeration was invented, keeping something cool when it was warm outside was the job of ice.  Ice would be collected during winter, transported to ice houses and stored until it could be sold for use in ice boxes.  The block of purchased ice would be put in the ice box and begin to extract the heat out of the air.  If the ice started out below 32 °F it would first warm up to it’s melting point (32 °F) and then stay at that temperature until it had melted completed.  While the block of ice could extract some heat before it started to melt, the vast majority of the “work” was done while the ice was melting.

With the advent of refrigeration, ice houses started producing their own ice rather than collecting it.  During this transition, it became intuitive to refer to amounts of refrigeration in terms of tons of ice produced within a single day (24 hours). A system that could produce 10 tons of ice every day had a 10 ton system.

Some quick math demonstrates how this simple expression become our modern definition:  The latent heat of ice (the energy it takes to freeze or melt at a constant temperature) is 144 Btu per pound.  If a ton is 2000 lbs, then it takes approximately 288,000 Btu to freeze one ton of ice.  Giving the system a day to create the ice you can convert 288,000 Btu per day to Btu per hour and you get the modern definition of 12,000 Btu/hr.

Eventually, home refrigerators and air conditioning reduced the need for dedicated ice houses and the trade disappeared.  However, we still measure refrigeration amounts in tons of refrigeration.  A home air conditioner is usually 1 to 5 tons while a home refrigerator is only around 1/4 of a ton.  Commercial systems can be as small as residential systems or chilled water systems with the tonnage in the hundreds!

Large refrigeration systems are often designed by the manufacturer.  However, it may make sense to have an engineer independently design or review system options to make sure that the system is achieving the owner’s goals.  With years of experience designing commercial refrigeration and HVAC systems, Forward Engineers can assist you in your next design, retrofit or remodel project. If you are seeking to work with an engineering firm that is client-centered and strives to provide services that are on time, on budget and exceed expectations, please contact us. We would love to work with you on your next project!

When considering upgrades to a building, one usually thinks first of high tech solutions. While these generally can solve the problem there are important factors such as increased maintenance and high installation cost that need to be considered. Some building issues may be solvable with “old world” solutions which may be much less expensive. For example, be sure to read our article on how to increase the insulation of a window without replacing it. While you are at it, you may want to revisit one of our older articles on keeping cool before refrigeration including strategies for reducing the cooling load on a building.

Here’s a few other topics we were talking about this month:

1. Home Dehumidification – A dehumidifer can keep your home or business more comfortable and maybe even save some money along the way.
2. Green Building Codes – What is a green building? It’s more than just the paint color.
3. Return on Investment – How do you know that a project will save money by saving energy? You just calculate the Return on Investment.

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One of the cornerstones of energy efficient design is that any project should be a good financial decision.  That is why I often describe our energy consulting services as a way to “save money by saving energy.”  Any decision to replace lights, HVAC systems, or even to retrain employees must be a good business decision.  Since many projects cost money up front, it falls to Return on Investment (ROI) calculations to show that money will be saved in the long run.

I primarily use what I call a simple ROI calculation.  All you need is two pieces of information: 1) How much does the project initially cost, or if the unit is due to be replaced anyway, what is the difference in cost over a direct replacement?  2) How much will the new equipment save in annual expenses?  At that point you can divide the initial cost by the annual savings to come up with how many years it takes to break even.  Whether the timeline is good or bad will depend on your business situation, but in general if it is less than the lifetime of the equipment then you have proven that some savings are available.

For example:  A business owner has a standard efficiency 5 ton rooftop air conditioner on their building.  The unit stops working and needs to be replaced.  Another standard efficiency unit will cost $6000, but the manufacturer also sells a high efficiency model for $6800.  The unit will save the building owner $200 a year in energy costs.  Divide the incremental cost of $800 by the annual savings and you calculate a simple ROI of 4 years.  The unit should last a minimum of 10 years so the building owner can expect to save a total of $1200 over the remaining lifetime of the unit.

More complex ROI or payback models could take into affect the time value of money (inflation), maintenance costs and incentive programs.  Projects should be worth enough that a building owner won’t make more money by simply investing their capital somewhere else.  Sometimes more efficient equipment can require extra maintenance and if this increases your expenses if should be included in the ROI calculations.  Incentive programs can really help an ROI by directly offsetting the incremental cost of a more efficient unit.  Going back to our example, if a utility rebate paid $400 for the installation of the new unit, the ROI goes from 4 years to only 2!

If you are interesting in saving money on your building by saving energy, consider hiring us to complete a Small Business Energy Audit.  We will review your building and provide you with options for saving money.  We’ll also review utility incentive programs to help cover the cost of the improvements. Our goal is to provide an affordable service that a business can use to reduce their energy costs.  We are happy to work with you to find a solution that fits your budget.  If you own or manage a building and are interested in an audit, please contact us today.