“Value engineering” is a term that is familiar to those involved in the design and construction of buildings and generally involves the substitution of a specified component or system with an alternative solution that is similar, but less expensive. Consider the following:
A building is designed to include a heat recovery ventilation system (HRV) in order to provide a balanced exchange of continuous fresh air to the occupants and, at the same time, transfer heat from the stream of warm air being exhausted to the cold stream of air coming inside. The design team chooses and specifies an HRV system that is rated at 90% efficiency at transferring the warmth from the outgoing stale air to the incoming fresh and filtered air. Let’s call this 90% efficient HRV, “System A”.
Before construction begins, the builder does some research and discovers that there is an alternative, HRV “System B”, that is available at a significantly lower price and is rated at 80% efficiency. The difference between 80% and 90% is only 10%, so it seems like a smart choice to give up a little in performance in order to take advantage of the savings opportunity.
The 10% drop in efficiency between System A and System B, as you can see in the green segment of the bars below, is a relatively small difference. To provide a specific example: Assume that the inside air temperature is 70 degrees and the outside temperature is 30 degrees, a difference of 40 degrees. System A would deliver incoming air that has been warmed 90%, to 66 degrees (36 degrees of the 40-degree difference), while the incoming air from System B would be 62% (32 degrees of the 40-degree difference). Again, the 4-degree difference between 66 and 62 degrees is relatively small.
However, when you look at the same comparison from the perspective of “inefficiency” (the pink segment of the two bars) you can see that HRV system A is 10% inefficient, while HRV system B is 20% inefficient. The heating load to make up a continuous 8 degrees of difference is double that required to make up the 4 degrees. HRV system B may save you money on the original purchase price but the additional 10% change in efficiency doubles the cost of heating, a 100% impact — year after year, for the life of the HRV system.
Do the math and make informed decisions about value engineering.
Author:
Jay Gentry
