Energy and Smart Building Industry Blog

Energy and Smart Building Industry Blog

Getting Back to Basics - 5 Assumptions Setting Back Your Setpoint Strategy

Friday April 5, 2019
By: Keith Gipson

We're really just getting back to basics.

There is a well established process for figuring out setpoints. We don't have to guess.

Note this is not talking about situations where there is something catastrophically wrong with the RTU. Those are actually pretty rare. Most of the time comfort issues are caused by incorrect configuration...starting with the setpoints. Both unoccupied as well as occupied.

Assumption  #1. "Whatcha see is whatcha get"

There's no sense going back and forth about what the unit SHOULD be able to do. Ideal or fictional scenarios. This is a real world, right now, pragmatic approach. This is a goal driven process.

The goal:

Make setpoint. The over arching goal is to run the unit a little as possible. 

The unit cooling or heating doesn't turn off until setpoint is made. "Set" unreasonable goals, and you will never achieve them. This is the "A" in S.M.A.R.T goal setting. Achievable. Only when the unit turns off mechanical heating or cooling, do you save energy. In controls speak the unit/zone is "satisfied".

Assumption #2. Making the occupied set-point is DEPENDENT on what the unoccupied set-point is set to.

This seems obvious, but in actual practice the unreasonableness comes into play. I like to take things to the extreme, for the sake of argument. 

For example, obviously in a cold climate setting the unoccupied setpoint to 30 degrees is ridiculous. Why? Because the interior would be frozen upon startup. 

But why in certain situations do we not think that 50 or 55 degrees unoccupied setpoint is just as detrimental to attaining the occupied setpoint? Is it because it's closer? Or within some arbitrary range?

The point here is that if the unoccupied setpoint is too LOW (in winter) or too high (in summer) you are in a permanent losing battle. AND you're making sure that you're going to waste the Maximum amout of energy possible. Guaranteed!

Why? Assumption #1. You're not making setpoint. So, the unit is running full out, trying to achieve the impossible setpoint.

In Building Engineer language you have now LOST the building. And blew your energy budget (you certainly are not saving energy). And people are most likely (very) uncomfortable. 

It's a lose-lose-lose situation.

Assumption #3 A temperature setback in the winter should be no more than 4-8 degrees.

This translates to 60 to 64 degrees. 

The unoccupied setpoint in the summer should be between 76 and 80 degrees.

Lower (in the winter) or higher ( in the summer) is not necessarily the best or even the most cost effective setpoint. Buildings have a certain design criteria and they are designed along with the mechanical systems to operate at maximum efficiency at a certain outside and inside temperature. And its most definitely not the lowest temperatures inside and out in the winter nor the highest temperatures, inside and outside in the summer. It's not that simple.

Assumption #4 The RTU in question seems to be working properly.

This is a pretty simple test. When 2 or more stages of heating are engaged HOT air is being blown into the space. And in summertime COLD air is coming out the register. Seems simple enough.

Assumption #5 Energy (in a building or anywhere else) is neither created nor destroyed.

Use energy NOW...or later. But you're going to use it. That is if you ever intend to actually make setpoint at some time in the near future.

If we have a choice, it's better to use energy earlier than later... Especially electricity which is billed on Time of Use and has a peak demand charge.

Now What?

The process for determining the proper setpoint for unoccupied as well as occupied is as follows:

Step 1. 

Starting point.

If it's heating season set the occupied heating setpoint to precisely 68 degrees and the unoccupied heating setpoint to 64 degrees. 

If it's summer set them to 72 degrees and 76 degrees respectively.

This is just a starting point. This process works no matter what the settings are.

NOTE***. DO NOT get over zealous or unreasonable. Start off conservative. TUNE the zone. Adjust in small increments until erratic or instability is introduced. Go back to the previous setting. STOP. 

We could (continue) to default to starting too aggressive with the setpoints, like a lot of companies and customers instruct us to do. But why subject our customer's employees and customers to a poor experience and drive up energy costs UP (and calls) - while we fix the configuration? They should be comfortable and we should default to not wasting energy and generating call volume while we figure this out. 

Step 2. Startup the unit. The RTU has 30 minutes to one hour MAX, to make setpoint.

Step 3. Evaluate the unit performance against goal.

Step 3a. IF the zone reaches the desired temperature within an hour, it's working.

Step 3b. If the zone does NOT reach the desired temperature in one hour max, then the unoccupied setpoint is most likely too aggressive. Too low in the winter, too high  in the summer. (This should be obvious by now).

Change the unoccupied setpoint by one degree each day, until setpoint is achieved. Once setpoint is made. Leave the unoccupied setpoint alone. 

Sometimes customers will have varying occupied setpoints. The instant the occupied setpoint is NOT achieved within one hour, readjust the unoccupied setpoint.

These two are interactive. 

This is how a building zone is "tuned". It is a continuous process. Before technology (EDX) came along, or even Direct Digital Control (DDC) BAS systems emerged, Building Engineers used this exact same process on old pneumatic controllers. 

This tuning process works for any control loop. Not just RTUs/AHU/HVAC. 

Boilers. Chillers. Manufacturing. Cars. Etc.

When a comfort call comes in, the first thing to determine is whether or not the has MADE the occupied setpoint. (Step #3) Not that the occupied setpoint is at some corporate standard. Remember the unreasonable 30 degree unoccupied set-point, or the 50 degree unoccupied set-point, there is no difference between the two of them. Both are unreasonable.

Step #3 and re-evaluation of the set-point is an ongoing process. Not making setpoint is an indicator that something is wrong with the configuration again.

This is what EDX and Adaptive Energy Management (AEM) is all about. It's a fancy term that really just automates this basic process.

This is not an "experiment". This is not anything new. This is how buildings are supposed to be managed. There's no need to extensively test this out. It works. 

Buildings have worked this way since the thermostat was patented by Albert Butz, founder of Honeywell, in 1886 or invented by college Professor Warren Johnson in 1885, founder of Johnson Controls.

"Getting back to the basics". That's what this is all about.

Posted in: Adaptive Energy Management