Formula for outdoor reset

Chuck Shaw_2

that you can plug variables into to show an outdoor reset curve on the x and y axis of a standard graph?

Thanks in advance for your time

Chuck

Mike T., Swampeast MO

Since the "curve" in most cases is a straight line, it's VERY simple. You only need to plot two points and draw a line.

Start with your design temps--both outdoor air and boiler supply.

Reset control (mechanical ones at least--and I presume electronic as well) will express reset as a ratio.

A ratio of "1" means that for each degree of drop in outside temperature, supply temperature rises one degree; a ratio of 1.5 means that for each degree of drop in outside temperature, supply temperature rises 1.5 degrees; a ratio of .5 means that for each degree of drop in outside temperature, supply temperature rises .5 degrees; etc.

If you're using a computer you only have to give two points so just enter a new point one degree in outside temperature away from the first.

If you're plotting the old-fashioned way, put a point say 20 degrees in outside temperature away and draw your line.

Tim Doran_2

Tekmar

E002 and E003 give some good info. www.tekmarcontrols.com

Tim D.

chuck shaw_3

I realize that mike,

what I was looking for was a formula that I could plug into an Excel spread sheet, so I could just enter different numbers, and have the curve change graphicly. I would want to use this to demonstrate how a heating curve could change, when giving presentations.

Chuck

jwade55_3

I've used this before.

Nothing spectacular, but gets the point across.

J

chuck shaw

Thanks Jay

thats what I was looking for, but couldnt get the graph to work the way I wanted it too.

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scrook_2

line formula

y=mx+b y is vertical axis, x is horizontal axis, m is slope (y/x) and b is the y-intercept, the y value when x is 0. For reset the slope, m will be negative.

Also you might use Excel's IF function for min and max boiler temps, i.e. the reset slope becomes flat at the min temp and at the high limit temp instead of using the formula.