Energy Wastage From Excessive Chiller Use


We (humanity) must get better at energy efficiency ... every kilowatt is going to become very important.

Energy security issues are in the headlines and climate change has been long discussed. So why are we not better at making our buildings more operationally efficient? Could it be that we don’t know how well our building energy distribution systems are actually performing?

There really is no excuse for us not to get this right. The data and analytics we can obtain nowadays make it simple to see what is happening in our buildings. Low cost IoT sensors capture data easily to help us manage space effectively.

The Case Study

Here’s a recent OPNBuildings example of energy waste in an office block where a chiller is running excessively.

The chiller starts at 6am, indicated by fall in flow and return temperatures. This is confirmed by the electrical consumption meter. The first question that comes to mind based on the chiller profile is, should this chiller be running at all? The loads are so low, on a 600kW chiller, it would suggest that mechanical cooling should not be provided. That said, even if it does have to run, there is scope to optimise operation.

Chilled water flow and return temperatures fall rapidly indicating very low load.

Building occupancy starts at 8am and increases rapidly at 9am as indicated by the CO2 profile chart below. CO2 levels drop off from about 4pm, which is consistent with the expected profile for an office building.

Considerable energy savings for a minimum of 3 hours per day are possible. Given a 600 kW thermal capacity, the electrical capacity will only be a small proportion of the full load - say 5 to 10 kW. But also consider the chilled water pump which is running continuously. This is likely to have an unnecessary cost of 30 kW each morning. This equates to about €12 per day – it all adds up!

CO2 dashboard levels start reducing at 4pm as people leave. A larger drop occurs from 5pm. To save energy, the chiller could be switched off at 3:30pm, leaving the secondary chilled water pump running until the chilled temperature rises to say 15º. More kW can be saved here, potentially a lot, if the chiller is fully loaded. Savings could be as high as 500 kW over the course of the shoulder and winter seasons.

OPNBuildings platform identified significant energy savings for this client with no impact on building performance. This result was backed up by high levels of comfort within the building and good fan coil unit performance.