How can your current BMS maintenance contract save you energy for 'free'?

You would be surprised at how little Building Management Systems maintenance contracts have changed in the past ten years. Maintenance contracts are still primarily set up for Periodic Preventative Maintenance.  

 
Lifecycle Controls Bryce Anderson independent BMS consultant
 

If we take a preventative maintenance contract and schedule in additional time for optimisation, tuning, mini projects, improved alarming, improved trending, recommissioning and updating out of date documentation, then the annual maintenance cost will increase, probably significantly, and to a point that the funding will not be available.

However, if we reshuffle the twelve month plan into a three year plan, but keep the same annual maintenance cost and hours, then we can shift energy efficiency tasks into the freed up days.

For example, systems that affect the entire building (chilled water, hot water and condenser water) should be checked every year through preventative maintenance checks. Systems that affect large areas (air handling units) could have preventative maintenance checks every second year. Systems affecting small zones of a building (fan coil units, variable air volume units and package units, etc) could be checked every third year. This will free up a significant amount of days each year.  

Personally, I usually use the first month or two of freed up days to reverse engineer documents that have been lost or not updated after the previous hardware upgrade ,then schedule in mini projects into the 'free' days. Without an up to date functional description it is near impossible to effectively optimise the control strategies.

This is still a reasonably conservative approach. If you have demanding energy improvement KIP’s, and you have had good quality preventative maintenance in the past, I would consider putting preventative maintenance on hold for twelve months and utilising the maintenance budget to embarking on an aggressive optimisation programme. BMS companies will usually support a reshuffle of their maintenance tasks, as long as you don’t reduce their annual contract value.

Other than reworking the maintenance plan, there are certain tasks that probably don’t need to be done at all. For example, tightening controller terminals every twelve months. When control panels are delivered to site, the terminals can vibrate loose; consider tightening them once every ten years. Some tasks are no longer relevant, for example, changing controller batteries; modern controllers don’t usually have replaceable batteries.

Then there are the highly debateable tasks, such as calibrating space temperature sensors. In my opinion, space temperature sensors should be calibrated once, and then probably never again. Space temperature sensors are usually 2-wire passive sensors, when the temperature changes, the resistance of the sensing element changes, the controller then detects this change in resistance, and converts it into a temperature reading. The purpose of calibrating a temperature sensor is to offset the resistance of the cable between the sensor and the controller. Temperature sensors are factory calibrated. My preferred method to calibrate the sensor (offset the cable resistance) is to put a fixed resister onto the cable at the sensor, and whatever the controller reads differently to when the resister is directly wired into the controller, is the effect of the cable resistance.

I also believe that calibrating a temperature sensor with a handheld thermometer can cause more issues than not. It is highly likely that the hole in the plaster board wall where the cable comes through was not sealed during construction. The temperature sensor can sometimes pick up a slight draft from within the plaster board cavity. This draft can be warm or cool, depending on the season. Calibrating the sensor from 23.0°C to 23.4°C across 300 temperature sensors can waste energy, as the equipment calls for additional cooling.  

 
 
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BRYCE ANDERSON

Lifecycle+Controls+Bryce+Anderson+independent+BMS+consultant

INDEPENDENT BUILDING AUTOMATION CONSULTANT 



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