CFOs and finance directors have invested heavily in solar panels and commercial battery storage in recent years to protect themselves against energy prices that have risen rapidly. However, in many cases, they don’t get the savings promised by their installers.
One reason is that the software controlling electrical equipment on site, such as a battery, may keep following the same instructions as electricity prices rise and fall and solar output and site demand go up and down.
In this article, find out what building energy management systems (BEMS) are, how they can reduce energy use and costs and what you need to ask installers and engineering, procurement and construction (EPC) contractors about the systems they recommend.
What is a building energy management system?
A building energy management system (BEMS) tracks when and where a building uses energy and what electricity costs at different times. It uses this information to find waste and ways to lower the building’s energy bills.
An installer can connect the BEMS to heating, lighting, batteries and other equipment. If the people running the site approve, it can then switch those items of electrical equipment on and off or adjust their settings automatically.
How does a building energy management system work?
Most BEMS follow four steps to find where a building could use less energy or pay less for it.
1. Collect
The system collects data from on-site meters, sensors and the building’s existing controls.
The main meter records how much electricity the site takes from or sends to the grid. Solar panels and batteries installed behind the meter can supply the building before the main meter records how much electricity still needs to come from the grid. Other meters can record how much electricity particular areas or pieces of equipment use. Sensors can record temperatures and whether rooms or work areas are in use. The building’s controls show when connected equipment is due to run and the settings it follows.
This information goes to a gateway at the site or an online platform, where the software can use it.
2. Analyse
The software looks for electricity being used when it isn’t needed and times when the site could buy power more cheaply.
It checks how much energy the site uses, its opening and closing times, which rooms or work areas have people in them, the weather and electricity prices.
The BEMS must also follow the limits set by the people running the site. For example, if an area must stay within a set temperature range, the BEMS won’t turn the heating or cooling down so far that the room becomes too hot or too cold.
3. Act
When the software finds a possible saving, it can alert the facilities team. For example, it may show that heating, lighting or other equipment is still running after part of the building has closed.
If the BEMS is connected to the controls and it’s been set up so that it can control equipment automatically, it can send instructions itself.
It may alter when equipment like heating, air conditioning or lighting switches on and off, adjust settings like the target temperature for a room or tell the battery controls when to charge and discharge.
4. Check
Once the equipment has followed the new instructions, the meters record how much electricity the site uses. The software then applies the prices in the site’s tariff to work out the cost.
The BEMS compares this with what the site would probably have used and paid if the equipment had carried on as before. This estimate is called the baseline and is based on readings from similar days. The difference shows whether the new instructions saved energy or money.
What can a BEMS control?
A BEMS will only receive readings from meters and sensors connected to it. It can only control equipment that the installer has connected and the people running the site have approved for automatic control.
Before accepting a proposal for your site, ask the installer or EPC to list:
- Which meters and sensors will send readings to the BEMS
- Which equipment it will control
- Which settings it can control
- How it will connect to the building’s existing systems
- What limits it must follow
You can then see whether it covers the whole building or only certain areas and equipment.
What is the difference between a fixed and responsive BEMS?
A fixed BEMS follows a timetable of instructions given to it in advance while a responsive BEMS uses the latest information from the site to adjust them throughout the day, helping the business use less energy and buy electricity when it costs less.
If the site has a compatible battery, the BEMS may also pass charging and discharging instructions from a battery energy trading provider.
What is a fixed BEMS schedule?
A fixed BEMS schedule is a list of times and settings programmed into the BEMS when it is set up. For example, it may tell the heating to switch on at 6am or a battery to charge overnight and discharge late in the afternoon. It does not deviate from this schedule. Charging the battery when electricity costs less and using the stored power when it costs more is called energy arbitrage.
The problem is that the site may not need the same amount of electricity at the same times each day. Solar output and electricity prices may also be higher or lower.
For example, a battery may be programmed to start discharging at 4pm. If electricity becomes more expensive at 2pm and cloud cover leaves the solar panels producing less power, the BEMS still waits until 4pm. The business buys expensive electricity from the grid for two hours even though the battery has power stored.
This is a particular problem in the UK and Ireland because the amount and timing of solar generation can be very different in winter and summer, while cloud cover can also leave output higher or lower than expected during the day.
What is responsive BEMS control?
Responsive BEMS control uses the latest readings and forecasts to recalculate battery charging and discharging times, heating start times and target room temperatures throughout the day.
On a warm morning, it may start the heating later. If electricity becomes expensive earlier than expected, it may bring the battery’s discharge time forward to cut down on what the site takes in from the grid.
For the battery, the BEMS checks how much electricity the site is using, how much solar power is expected, what electricity costs and how much power the battery has stored. It can update the charging and discharging times, but it can’t use any battery power that the people running the site have told it to keep in reserve.
Take the earlier example of electricity becoming more expensive at 2pm rather than 4pm. If solar output was down because there was cloud cover, a responsive BEMS might bring the battery’s discharge time forward to 2pm. The battery then supplies the site during the expensive period, so the business buys less electricity from the grid.
This is useful for UK and Irish sites with solar panels and batteries. On a cloudy winter day, the BEMS may keep more battery power for the expensive evening hours. On a sunny summer day, it may leave more room in the battery to store solar electricity produced during the afternoon.
How much can a BEMS save?
How much a BEMS saves depends on your building, the equipment it controls, how that equipment operated before and what the installer has allowed the system to adjust.
There is research into what BEM-controlled systems can save:
- Energy savings of 10% to 12% with one type of underfloor heating during cold winter months
- Savings of up to 30% on heating, ventilation and air conditioning when BEMS make decisions based on weather forecasts, sensors and computer models
- Installing modern sensors and controls could reduce their total energy use by up to 29% (measured by sector rather than individual buildings)
These percentage savings don’t apply to your whole bill, just the energy use covered by each study. So, for example, if heating and cooling account for £40,000 of a £100,000 bill, a 10% saving on heating and cooling would cut the whole bill by £4,000.
Can a BEMS reduce the cost of connecting EV chargers?
Sometimes. Every site has a limit on how much power it can take from the grid at one time. Adding several EV chargers may take the site above this limit, meaning the business may then have to pay the network operator to increase it.
If the site has a battery, the BEMS software can send an instruction to the battery inverter when several vehicles are charging up. The battery will then supply some of the electricity, reducing how much the site takes from the grid. Using a battery to reduce the most power a site takes from the grid at one time is called peak shaving.
This may allow the business to install more chargers without paying for a larger grid connection straight away. However, the battery must be able to supply enough power for as long as the chargers need it. If it can’t, your site may still need a larger connection.
What should you ask before choosing a BEMS?
What you need to check depends on whether the BEMS will control equipment you already own or form part of a new solar and battery installation.
| Question | Adding it to equipment you already own | Buying it with new solar panels and a battery |
|---|---|---|
| What will connect to it? | The supplier should check your meters, sensors, battery, inverter and controls. It should then tell you what can stay and what must be added or replaced. | The proposal should list every meter, sensor and item of equipment the installer will connect to the BEMS. |
| What will it control? | The supplier should name every item the BEMS can switch on and off and every setting it can adjust. | The installer should explain how the BEMS will control the battery, solar system and any other equipment included. |
| How did you work out the saving? | The calculation should use your actual energy use, tariff, opening hours and current battery performance. | A commercial solar calculator should use your site data and show the savings from solar, the battery and responsive control separately. |
| What if the site doesn’t run as expected? | The supplier should show what happens if your energy use, electricity prices or solar output are higher or lower. | The installer should show what happens if the solar panels produce less power or the site uses more electricity than expected. |
| How will we know whether it worked? | The supplier should compare the new results with what your equipment would probably have done without the BEMS. | The installer should report how much electricity the solar panels produced, when the battery charged and discharged and what the site paid for electricity. |
| What happens if the software or internet connection stops working? | Your existing equipment should keep running safely using settings agreed before installation. | The installer should explain how each item will continue working until the connection returns. |
Could GridVolt improve how your current or planned energy setup works?
Energy Manager is GridVolt’s version of a BEMS. It can connect to compatible batteries, solar systems, EV chargers, heat pumps and building controls from other manufacturers.
If you already have this equipment, GridVolt can check what Energy Manager could connect to and control. If you’re planning a new solar and battery setup, the GridVolt simulator can estimate how much Energy Manager could add to the savings before you buy.
Energy Manager uses your site’s electricity use, tariff and expected solar generation to calculate when connected equipment should run. It updates its forecasts 96 times a day and calculates new instructions every 15 minutes.
At one agricultural site, Energy Manager increased the savings made by the battery by 41% in its first 70 days. That was a 41% increase in battery savings, not a 41% cut in the site’s whole electricity bill.
For suitable sites in Great Britain, GridTrade works alongside Energy Manager. GridVolt may then use compatible battery capacity left after the site’s needs to earn trading income. This income is separate from the savings on your electricity bill.
Tell us what equipment you already have or what you plan to install. GridVolt can check whether it is compatible and show what Energy Manager could control.
To find out more, fill in the form on the right, or get in touch via our contact page.
Note: Article image courtesy of Nova.lv
Frequently asked questions
BMS vs BEMS: what’s the difference between a BMS and a BEMS
A building management system (BMS) keeps services such as heating, cooling and lighting running safely and comfortably. A building energy management system (BEMS) looks for ways to use less energy and lower costs.
The two systems can work together, and some products do both jobs.
| BMS | BEMS | |
|---|---|---|
| Main job | Keep building services safe, comfortable and running as planned | Find ways to use less energy and lower energy costs |
| Information it uses | Room temperatures, whether areas are in use, equipment settings, running times and fault warnings | Meter readings, electricity prices, solar output, weather forecasts and information from connected equipment |
| Equipment it commonly covers | Heating, cooling, ventilation, lighting and alarms | Meters, solar panels, batteries, EV chargers and equipment connected through the BMS |
| What it can do | Switch connected equipment on and off and keep it within its approved settings | Alert the facilities team or automatically sends instructions to power on or off or change settings to particular equipment |
| How they work together | Provides many of the controls used to run the building | Uses energy and cost information to decide changing equipment running times or settings could save money |
There isn’t a fixed line between the two. Some BMS include energy-management features, while some BEMS connect to the BMS already in the building. If you’re considering installing a system, ask the installer what features the software they’re proposing for your site includes.
BEMS vs BACS: what’s the difference?
A building automation and control system (BACS) monitors and controls equipment around a building. For example, it can switch heating and lighting on and off at set times and keep rooms within a set temperature range.
A BEMS has a more specific job. It checks how the building uses energy and what that energy costs, then looks for ways to cut waste and lower bills. It may use controls that are already part of the BACS.
Some systems do both jobs. Ask the installer exactly what the proposed system will monitor and control.
Is a BEMS hardware or software?
According to the UK government’s Energy Technology List, a BEMS can be stand-alone hardware, software or a combination of both. Software still relies on meters, sensors, controllers or a BMS to collect data and carry out any approved changes.
Does a BEMS replace an existing BMS?
Usually not. A BEMS often connects to the BMS and other site equipment so it can analyse energy performance across them. The BMS can continue to handle the direct control of heating, cooling, lighting and other building services.
What is the difference between energy monitoring software and a BEMS?
Energy monitoring software shows how much energy the building used and when it used it. A BEMS is a type of energy management software that can also calculate new running times or settings for connected equipment.