Posted by: lcowie | November 16, 2010

Outdoor Design Temperature

Did you know that your heating or cooling appliance won’t be sufficient for a portion of the time that you are using it? Don’t fear – that is how it is programmed to work. There’s really no great way of getting around it. You can certainly try to program your appliance to work at all times, but it will come with some consequences.

According to the Building Performance Institute, your heating or cooling appliance should be programmed to an outdoor design temperature. If it is not, then your appliance is likely too large. The problem with an oversized unit is that it uses more energy over time. A smaller unit will be more efficient; there will be a spike in energy use, simply because the unit will have to overcome the heat or cool naturally inside the appliance, but after that, the energy use will level out. This is why you program the unit to adhere by BPI’s outdoor design temperature.

In the winter, the heating temperature for your appliance will be above the outdoor temperature 99% of the time. So, if you live in Denver, CO, and the coldest day in the year is -11 degrees, your “outdoor design temperature” is going to be -7 degrees. After -7 degrees, the unit will not be as sufficient (or hot) as you’d like.

On the other hand, if you live in Yuma, AZ, and the hottest day of the year is 123 degrees, your outdoor design temperature will be 114 degrees. There is a 1% margin of error, if you will. If the day is warmer than 114 degrees, your unit will not sufficiently cool you.

There are only a few instances during the year where you have to worry about this. I suggest adhering to the outdoor design temperature. It will not be -11 degrees or 123 degrees every day. The system will not work 1% of the time, or 88 hours. If you don’t adhere to the outdoor design temperature, your unit will likely be too large, and that will cause you a variety of other problems!!

Leave a comment if you’ve got a helpful example in which your appliance was designed NOT to work at a specific temperature. I’d be interested in hearing how you dealt with the situation!


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