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  • Writer's pictureCatherine Bottrill

Save energy out of hours

Updated: Jun 28, 2023

An an auditor with many buildings under my belt — from offices to art galleries to opera houses — I am always surprised by the frequency with which I see unaccountable energy being used when the building is nominally closed. In my experience this is often 20% but can be higher. In the best run buildings it is always negligible and this has occurred because thought has gone in to how the building operates.

The following strategies are ways of giving yourself a 20% energy reduction without too much effort and usually little or no investment!

Set a target

What should your building be using out of hours? If you add up the powers of everything that should be on — alarm systems, emergency lighting, fridges, freezer, servers, CCTV etc you will get a number that you can express in kW. This is the target you should be aiming for in your subsequent actions.

Monitor your energy use

If you don’t have a smart meter, then you can measure the energy used overnight by reading your meter as you close up the building one night and open it the next morning. Take the latter reading away from the former and you have your energy us in kWh. Divide this by the number of hours and you have your average power that can be compared with your target found above.

If you have a smart meter, you will be able to get your ½ hour meter data directly off either your supplier or whichever energy monitoring system your meter is connected to ( offers such a management system). These platforms usually give the electricity used every half hour and the average power over that half hour is found by doubling it. This can also be compared to your target above.

Better use of smart meter data

Smart meter data is far easier to use than manual meter readings and a lot more powerful. When you look at the graphs, look out for the following

  1. Does your building energy use jump as staff come in and the building opens — or several hours before as is common when cleaners come in early?

  2. Does your building energy use drop as the building closes — or sort of tail off over a few hours? Something isn’t right if it does.

  3. Does your weekend use look like your night use or your weekday use? If you are closed at the weekend but your weekend energy looks like a weekday then it is a settings issue with your BMS or timeclock.

  4. What do back holidays look like? What do you think they should look like?

Half hour electricity data from

Common loads found overnight

  1. Lights left on

  2. Air handling — need to check this in the BMS

  3. Split system air conditioners — set by remote control and running overnight

  4. Computers and monitors — could be half a kW each and a room full of office staff this could be a third of your energy use running computers overnight — use saving settings or switch off

Torchlight surveys

Torchlight surveys involve walking through a building out of hours and finding what is on (often with a torch). It’s a good time to heat pumps, motors and fans and if your building is closed you know it's either on for a reason or should be off. Torchlight surveys inevitably find waste. Every item found on that shouldn’t be — make a note and turn it off. You can check how close you are to your target in a few days.


How to prevent things being on that shouldn’t be?

  1. Proper BMS settings — the BMS schedule should match the activity of the building and be changed when the building changes.

  2. Use cleaners or security with simple instructions — when you see something on between x pm and y am then turn it off.

  3. Use a ‘building closer’ — a member of staff who is the last out (usually on a rota) to manually turn everything off.

  4. Timeclocks — work especially well with lighting systems. Seet the on/off time and forget.

  5. Manual override — popular in some shops. Everything apart from the alarms, emergency lights and till (which needs overnight updates) is connected through a single key operated circuit break — off every night and on every morning.

  6. Keep and eye on split systems — take the controller away from staff, switch off manually every night.

In summary, out of hours use is usually high, it is quite simple to locate and simple to remedy. Why not give yourself 20% energy savings for such little effort!

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