The value of interval data in effectively managing your consumption can not be overstated.
Interval energy data contains a lot of information about a building's energy usage.
But what exactly is interval energy data, how do you get it, and why should you be interested?
Interval energy data is a fine-grained record of energy consumption, with readings made at regular intervals throughout the day, every day.
Interval energy data is collected by an interval meter, which, at the end of every interval period, records how much energy was used in the previous interval period.
Such data is often referred to as "interval data", "interval meter data", "demand interval data", "kW interval data", "electricity interval data" (electricity interval meters are particularly common), and other such variations. Common forms of interval data include 15-minute data and half-hourly data.
Why Should We Be Interested in Interval Data?
If you're an energy user (a business or other organization), your interval data is invaluable for the energy management that can help you to reduce your energy consumption. It will help you understand how much energy you are using and at what times of day, understanding this is the first step towards optimising it. Are you using more at night time when the building is empty than you expected? what is happening every Sunday that causes that spike of usage? Being able to visualise your data leads you to ask appropriate questions and focus on where wastage is likely to be found.
Where Does Interval Data Come From?
Interval data comes from interval meters. In the last few years it has become very common for medium- to large-sized buildings to have interval metering.
Broadly speaking, such metering systems are usually one of two types:
1. An interval meter from the energy supplier or utility
In many countries and states, utilities are required to supply and manage interval meters for all electricity customers over a certain size. For example, UK energy suppliers have to provide their larger customers with half-hourly metering, as explained in the page on half-hourly data.
It is common for energy suppliers or utility companies to provide their larger customers with a free interval meter. In some countries or states this is mandatory (see right), but suppliers often do it anyway, as the detailed interval data helps them with billing and demand forecasting.
As well as using the meter data themselves, suppliers / utilities typically also make the data available to customers that request it for energy management purposes.
It's most common for utilities to provide interval electricity metering, but some utilities also provide interval metering on gas supplies. Energy Lens works with any interval energy data, whether it's from electricity or gas.
If you are the energy customer, or working on their behalf, you can contact the supplier or utility to find out how to get the interval data from them. An authorized person can usually request that the supplier email them data (e.g. for the last month or the last year), and some suppliers have a website from which customers can download their recent interval energy data.
2. A private metering system
An private metering system is often installed by the organization occupying the building, by the property managers, or by a third party that leases the system to the tenants or managers.
There are many different forms of smart-metering systems installed in buildings, but essentially they have the following components:
Meters – these are placed on electricity and gas supplies to monitor the energy consumed.
Loggers or logging software – these keep a record of data from the meters, and typically offer the means to export the stored interval data in a format that Energy Lens can work with. They often offer some analysis features as well, but these are usually pretty basic.
These private metering systems are typically the best form of interval metering:
They usually have multiple meters recording data for separate areas of the building(s). The more detailed the energy consumption data, the easier it is to identify routine waste and to track progress at reducing it.
They will typically collect interval data for gas as well as electricity. They sometimes also meter other forms of energy such as heat.
If the building has a smart-metering system, the interval data should be readily available through that system.
How often should a business monitor their interval energy data?
It is typically worthwhile to look at fresh data at least once a month. So, once-a-month the business would:
Obtain the interval data for the previous month.
Study the data to discover any energy wastage that may have occurred, and to compare the last month's energy performance with that of previous months.
Take steps to prevent further wastage, and to further improve energy performance.
It may be beneficial to perform a similar routine more frequently, maybe once a week.
How to Use Energy Profiles to Find Energy Waste
The patterns (or profiles) of energy usage contained within interval energy data are great for discovering where a building is wasting energy. The fine-grained detail of interval data (such as half-hourly data) is key – daily, weekly or monthly data doesn't carry anywhere near as much information about how energy is being used.
Energy profile charts and how to create them
Patterns of energy usage are often referred to as energy profiles. An example of a month's worth of energy profiles is shown below:
How to create energy profiles from interval data
The charting features of Microsoft Excel will allow you to create your own energy profiles from interval data. However, you may wish to make the process faster and easier with specialist software. The graphs in this blog have been produced using the Energy Lens software produced by BizEE, a great tool to enable routine analysis of your interval data.
How to look at energy profiles – a general philosophy
Looking at energy profiles to find energy waste requires you to have some knowledge of the way that the building is operated. The key is to try to link the patterns of energy usage with the operations of the building.
Energy profiles show how much energy is being used at particular times-of-the-day and days-of-the-week – you want to be able to have a pretty good idea of what equipment is using that energy, and why it needs to be using it at the times in question.
If the profiles show energy being used on times or days when you're not aware of a good reason for energy to be used, that's an indication that energy is possibly being wasted, and something for you to investigate.
Understand the building to understand the energy profiles
To make sense of the energy profiles, you need to have good idea about what goes on in the building. Not everything that goes on in the building, just the things that relate to energy consumption.
Every building is different, but the following factors are commonly relevant:
Occupancy – when people come and go
What are the core occupancy hours (e.g. 9 to 5)? Are there multiple shifts (e.g. a day shift and a night shift)?
Do people ever work on-site outside of the core occupancy hours? Do certain staff stay on after the official closing time? Does anyone come in on weekends or holidays?
HVAC – heating, ventilation and air conditioning
What fuels are used for heating (e.g. gas, electricity – see note below)?
Is there air conditioning? Is it used just for cooling in summer, or is it used all year round (e.g. to keep equipment cool)?
How is the heating controlled? Is it on a timer? When is it set to switch on and off? Are there different timer settings for weekends and holidays?
It's important to be aware that most forms of gas heating also use electricity for fans, pumps and controls. For example, for a heating system consisting of a gas boiler connected to radiators, 5% or more of the total energy used will typically be electricity. This is particularly significant in cost terms because electricity usually costs several times more per kWh than gas.
Heating systems that involve ducted air will typically use a considerable amount of electricity (40% or so is not uncommon). Air conditioning also usually consumes a lot of electricity.
The upshot of this is that HVAC energy wastage can usually be identified from patterns of electricity consumption alone. But if you do have interval metering on your gas supply it's well worth taking a closer look at your patterns of gas consumption too.
Lighting
What controls when the lights come on and off? Are they automatically controlled (e.g. by a sensor that detects movement or light-levels), or are they turned on and off by staff?
Do lights remain on when they're not needed (e.g. when staff have gone home, or when they're on lunch-break)?
Are there enough light-switches? For example, if one person is working late in a large open office, will they have to light the entire office just to light their desk?
NB Most buildings have different sets of lights for different purposes (e.g. a set of lights in the main office, a set of lights in the meeting rooms, a set of lights in the warehouse, a set of security lights outside). Your answers to the questions above may depend on which set of lights you're talking about.
Office equipment
Do staff turn their computers off when they leave work?
Is there office equipment such as photocopiers / printers? Is it turned off when not in use?
(NB Whilst interval data is perfect for looking at larger patterns and trends, it won't help you to figure out how much energy an individual computer or photocopier uses... For that task you'll want to plug a simple plug top load meter between the equipment and the wall socket.)
Other energy-consuming equipment / processes
This could include anything from a printing room, to a fork-lift-truck charger, to specialist production-line equipment.
What processes or items of equipment exist that use energy?
What sort of energy do they use (e.g. electricity, or gas, or both)?
When do they use energy? When do the processes run? When is the equipment switched on and off?
It's important to note that industrial processes can often dwarf all other types of energy consumption in a building. If a building has processes or items of equipment that consume a lot of energy, even small changes to the way that they're operated can often make a big difference to the energy bill.
Examples of energy waste shown in energy profiles
If you've read the previous sections of this article, you should already have a pretty good idea of the sorts of patterns to look for in energy profiles. Following are a few examples of energy waste, and the energy profiles that help to identify them:
High out-of-hours energy consumption
Energy wastage is very common during "out-of-hours" periods (e.g. at night and on weekends). For example, the figure below shows a section of a calendar plot created using half-hourly data from an office building:
This example strongly indicates that out-of-hours consumption is excessive. In the out-of-hours periods (Thursday night, Friday night, Saturday and Sunday), the building is using around 35% of the energy that it uses in peak consumption periods.
It is often necessary for a certain amount of equipment to operate during out-of-hours periods (e.g. security lighting or a central computer room). However, it's rare for the out-of-hours consumption to need to be as high as is demonstrated by the above figure. Such patterns indicate that there is huge potential to save energy by reducing the out-of-hours energy consumption. Whether the cause is time scheduling having been overridden or the equipment is scheduled to operate 24 hours per day this is an important source of waste to tackle.
Poor automatic control (especially HVAC)
Energy uses such as HVAC (heating, ventilation and air conditioning) should usually be closely tied to the occupancy hours. Considerable energy is wasted if a building is heated or cooled when nobody is using it, or if an entire building is heated or cooled when only a couple of rooms are in use.
Below is a section of a calendar plot for an office. It looks like some equipment (probably the heating) came on automatically on an unoccupied
public holiday (Monday, 22nd April 2019).
The figure shows that the profile for the holiday Monday was different to that of the other weekdays nearby. Less energy was used over the daytime hours because nobody was in the office using equipment such as lights or computers. However, a fair amount of energy was used, even though the building was unoccupied. This indicates that something was erroneously set to come on automatically, heating being the most likely suspect.
A more severe example would be that of a building with a heating timer that only allows a single on-time and a single off-time (as opposed to allowing different times to be set on different days). It's not uncommon for buildings to have such a timer, even when they operate on Monday to Friday only – this results in considerable wastage as the heating comes on unnecessarily every Saturday and Sunday.
There are many, many conservations that can be applied, to make significant early wins in your energy conservation journey. Head over to the solutions pages to equip yourself with a treasure trove of initiatives.
Comments