Baseload Electricity Consumption
Electricity baseload is the background electricity usage a building has when it is unoccupied, and is typically caused by appliances which have been left on, appliances on standby, security equipment, lighting and is often dominated by ICT servers. Because schools are unoccupied for 85% of the year (holidays, weekends, before 8:00 and after 17:00 on a school day), a small improvement in the baseload can make a large difference to a school’s energy consumption, cost and carbon emissions.
A reduction in the electricity baseload of 1kW, equates to an annual electricity consumption reduction of 8,760 kWh (1 kW * 8,760 hours in a year), which is a potential saving of £1,051 per year if electricity costs 12p/kWh. Simply upgrading a couple of ICT servers which currently consume 750W each to ones which consumer 250W could save £5,000 over 5 years.
Energy Sparks calculates the baseload by looking at the energy consumption in the middle of the night when the school is unlikely to be occupied (after 10pm).
Out of Hours Electricity Usage
Schools have relatively high out of hours electricity usage mainly because of high baseloads (see above) in the 85% of the year when the school is closed (holidays, weekends, school days before 8:00 and after 17:00). The average out of hours consumption for a school is about 50% – so 50% of a school’s electricity usage occurs when the school is empty. Recommendations for reducing this cost, are very similar to those outline for the section on baseload above, plus trying to minimise usage at weekends and during the holidays where there is potential to turn off more appliances during the day.
Change in School Day Electricity Consumption
Electricity usage during school weeks should be relatively consistent over time, with a general increase in the winter because of additional lighting and for example boiler pump electricity consumption. However, you would not expect to see a significant change from week to week. If there has been a change then you might be able to track it down by comparing intraday graphs of electricity consumption, to see at what time of day there has been a change in usage. The largest users of electricity in school are ICT equipment and lighting, although it is unlikely these are the causes of change in electricity consumption from one week to the next. More likely candidates are items of equipment accidently left on – this will show up as an increase in the out of hours (baseload) usage.
Annual Electricity Consumption Compared with Benchmarks
On average schools use about 200 kWh of electricity per pupil per year (about £30/pupil) or about 50 kWh of electricity meter squared of floor area (m2). Electricity usage in schools increased significantly from 1990 through to about 2010 largely as a result of increased ICT usage, particularly the installation of servers. Since them usage has dropped as servers have become more energy efficient, energy hungry desktop PCs have been replaced with laptops and tablets, and some schools have started replacing their older energy inefficient lighting with more modern florescent lighting and LEDs.
Annual Gas Consumption Compared with Benchmarks
On average schools use about 350 kWh of gas per pupil per year (about £30/pupil) or about 115 kWh of gas meter squared of floor area (m2). Gas usage in schools has been dropping over the last 3 decades as a result of installing more energy efficient condensing boilers (typical saving 15%), double glazed windows and better insulation. However, unfortunately, newly built schools which should have lower energy consumption than older schools have the same gas consumption as their older counterparts. So, if you are working in an older school then its relatively poor fabric is not a justification for mot attempting to reduce gas costs. The biggest savings in gas consumption can be made by making sure heating and hot water are turned off during weekends and holidays, and by turning thermostats down (every 1C reduction in the temperature in a schools should reduce gas consumption by about 10%).
Out of Hours Gas Usage
Out of hours gas usage at schools varies significantly, and is perhaps one of the easiest, and cheapest ways of saving significant amounts of energy. Many schools leave heating and hot water on over weekends and holidays when it is generally unnecessary. If the school’s boiler has frost protection for instance there are often not good reasons for leaving the heating on.
Change in Gas Usage
The main cause of a change in gas consumption at a school is as a result of a change in the external temperature. A school’s heating requirements are directly proportional to the difference between inside and outside temperatures. So, for example if the inside temperature is 20C, and the outside temperature goes from 10C to 0C it is likely that gas usage will double as the temperature difference has doubled from 10C to 20C. When detecting changes in gas usage Energy Sparks tries to compensate for changes in external temperature before sending an alert. Changes in gas consumption are often caused by changes in the internal temperature of a school, a 1C increase on the thermostat leads to about a 10% increase in gas consumption.
During the summer when the heating is switched off and gas is only used for heating and possibly in the school kitchen there shouldn’t be much change in use from day to day, so an alert during the summer is more likely to be as a result of something changing in the school which impacts gas consumption. Suggestions might be if a hot water tap has been left on, or the control of the hot water system has been reprogrammed.
Weekend Gas Usage
There are generally few good reasons a school should be using gas at the weekend, unless there are weekend events. Schools should look to minimise weekend gas usage to zero. Generally the only justifiable reason for using gas at the weekend is for frost protection, which should only come on when the outside temperature drops below 4C, when there is a risk of water pipes bursting. The Energy Sparks automatic alert which reports weekend consumption will only report usage where the outside temperature is above 4C.
Reducing Energy Usage During Holidays
Up to 50% of most school’s energy is used outside school hours and a significant proportion is used during school holidays. Energy Sparks sends an alert just before a holiday to remind schools to prepare for the holidays by switching off as much unnecessary equipment as possible. Our advice it to develop a checklist which would provide a list of items which should be switched off on the last day before a holiday. This list could include:
- Heating: most school boilers have frost protection built in, so boilers for heating should be switched off, as it will save a significant amount of energy and cost. If the school is to be occupied by a few members of staff only, it is better for provide those staff with electric fan heaters, rather than heating the whole school, or if the school’s heating is zoned just leave the occupied zone on. Some schools have an egg-timer type boost control which allows staff who come in outside normal hours to turn the heating on foe between 30 minutes and 2 hours
- Hot water: hot water systems can be turned off to save energy. Please remember however to flush the system before the school is occupied again to reduce Legionella risk – you need to do this whether or not you have turned the heating off over a holiday (office HSE advice on Legionella here (TBD))
- Appliances: there are lots of appliances which are unnecessarily left on over holidays in schools, please come up with a list of those which can be switched off, particularly ICT equipment, and for example fridges and freezers in the kitchen (if food needs to be left in a fridge for example, first of all check whether it is necessary and won’t go off over the holidays, and secondly if there is more than one fridge or freezer can food be consolidated into a single appliance, and the remaining spare appliances turned off?
Turning heating off when warmer weather forecast
Sometimes during the Spring when the temperature increases schools forget to turn the heating off. Energy Spark provides schools with automatic alerts if warmer weather is forecast over the next 5 days.
Efficiency of Hot Water Systems in Schools
Gas based hot water systems in schools are often very inefficient, with efficiencies of perhaps 15% compared with the 80% efficiency of a domestic gas combi boiler. Most commonly in schools hot water is circulated permanently round a loop of pipework which covers the whole of the school, so when a hot water tap is turned on, hot water doesn’t have to come a long distance from the boiler room, but merely from the nearest section of circulating pipework; this considerably speeds up how quickly hot water comes out of the tap when its turned on.
The downside of this approach is that there are long sections of pipework, however well insulated, where heat can be lost. There are no simple low cost solutions to solving this problem completely. The best approach is to minimise the time the hot water system, and particularly the circulation of hot water to the periods when the school is occupied. In addition, if possible at low cost, pipework where uninsulated should be insulated.
The better longer term solution is to replace the circulatory hot water system with (electrical) point of use hot water heaters, which don’t lose as much heat. This could be done either as a one off, or gradually everytime toilets are refurbished.
Heating coming on too early in the morning
It is common in schools for the heating to come on too early in the morning. There are a couple of common reasons for this:
- Mis-programmed boiler: the start time for the boiler is set too early
- Problem with ‘Optimum Start Control’: most larger schools have a feature of the boiler controller called ‘optimum start control’ which automatically turns the boiler on earlier in the day in cold weather and later in milder weather. Most of these systems ‘self-learn’ when the best time is to start the boiler in order to get it up to temperature for when the school is occupied (e.g. 08:00). This learning is based on previous experience of how long it took in the past at different inside and outside temperatures. However, at many schools this automation doesn’t work properly, and turns the boiler on too early. The most common cause is the positioning of the boiler thermostat, often in cold areas e.g. halls or corridors which never get up to the required temperature in cold weather either because they are badly insulated, the radiators are not adequate or the radiators are turned off or TRVs set too low
Generally heating boilers shouldn’t be turning on before 05:00 in cold weather and 07:00 in milder weather.
Poor Thermostatic Control
The Energy Sparks dashboard analyses the quality of the thermostatic control in a school by looking at how linearly the annual gas consumption when the heating is on varies with outside temperature. For a school with good thermostatic control there should be a strong correlation between how cold it is outside and the daily consumption. This is measured using a mathematical representation of the divergence of the school’s actual gas consumption from that predicted by the outside temperature. This measure is called R2 (see reference TBD). The higher the R2 measure the better a school’s thermostatic control, any value above 0.8 is a good figure, values nearer 0.2 suggest the control of the heating is very poor.
Fixing poor thermostatic control can be difficult:
- sometimes it is caused by the boiler controller not working correctly
- sometimes it is caused by a poorly located boiler thermostat e.g. in a corridor
- often is it caused by windows being opened, and radiator TRVs being poorly set