The All-Electric Building
Senior Engineer, Henry Metcalfe, explains his thoughts on the electrical challenges of electrification.
As we get closer to our 2030 and 2050 Net Zero targets, it’s clear that all-electric buildings will play a key role in decarbonising the built environment. The predicted carbon emission factor is predicted to reduce from 0.136kgCO2/kWh to 0.053kgCO2/kWh by 2030 and 0.015kgCO2/kWh by 2040 (BEIS); whilst natural gas will remain at 0.210kgCO2/kWh. Senior Engineer, Henry Metcalfe, was invited to present a recent case study (Convent Way) and his thoughts on current industry issues at the CIBSE Build2Perform Live 2022 session and during a webinar as part of their #GrowYourKnowledge series. Henry was interviewed and helped write an article for the CIBSE journal to present the Convent Way project and the process undertaken to reduce the heating and electricity demand on-site using Passivhaus principles. When covering this topic, there are many directions one can take. Below, Henry provides his initial thoughts as an introduction to this subject matter.
There are several ways to electrically heat buildings and there are different strategies depending on the site. The first popular introduction to electric heating came in the form of direct electric panel heaters and electric storage heaters which used dual-metered supplies to benefit from off-peak electricity prices. These solutions are often the easiest to implement and most familiar for end users. Electric panel heaters are efficient in that there is little wasted energy producing a load that is mostly linear. There are however some disadvantages to this approach such as limitations on diversity at scale and low energy performance when compared to heat pump alternatives.
Heat pump solutions come in many guises, and manipulate the temperature, pressure, and energy content of refrigerants and utilise their low boiling point to transduce energy into a usable thermal output. Using the attributes of refrigerants, high coefficients of performance (COPs) of 4 to 5 can be achieved. Simply put, for every 1kW of electrical energy in, we can output 4 to 5kW of thermal energy. These systems are becoming more popular and as such, the significance of the learning curve for installers and end users is decreasing. Diversification of heat at scale is often easier to justify and calculate with heat pump systems and will therefore play a key part in reducing and decarbonising heat demand.
Although the answer to the heat challenge is most likely through heat pumps, it is important that we do not rely on high equipment efficacies but instead drive demand reduction through passive building design. When carrying out load assessments and predicted electrical energy demands, the key item when considering electrical usage of heat equipment is the heat loss of the space.
“It is important that we do not rely on high equipment efficacies but instead drive demand reduction through passive building design.”
With a UK target to deliver 600,000 heat pump installations per year by 2028 in homes and public buildings, the point of concern electrically is not only peak demand but electrical harmonic distortion. Harmonic distortion is calculated as the deviation from the regular sinusoidal waveform of AC electrical distribution. It is caused by non-linear loads which do not match the waveform of the supply. Harmonic distortion is calculated for each fundamental frequency of the supply and this is used to calculate the total harmonic distortion of the load. QODA has built a digital tool to calculate this distortion, highlight the worst-performing fundamental frequency, and indicate the harmonic current and voltage as a result of the total distortion of the system. It is important to understand the impact of this distortion as this will impact the size and arrangement of the electrical distribution and indicate whether there is a need to introduce harmonic filtration equipment. If left untreated, significant harmonic distortion can cause overheating and thermal damage to equipment and cabling.
When connecting to the National Grid, any potentially disturbing loads must be acknowledged and reported. The Energy Networks Association (ENA) maintains a list of equipment that has been approved for convenient compliance checking, however, if not on the list, the following items must be provided by the manufacturer.
- Datasheet and power quality documentation
- Harmonics to BS EN/IEC 61000-3-2 and BS EN/IEC 61000-3-12
- Flicker to BS EN/IEC 611000-3-3 and BS EN/IEC 61000-3-11
Despite certification compliance, there are some heat pumps that have a harmonic distortion greater than the advisable allowance. Unfortunately, this is not unique to heat pumps and is also present in the electric vehicle industry. Studies have been carried out on multiple electric car manufacturers and despite certified compliance with the IEC 61000-3-2 and -12 standards, when tested in practice, a large number of vehicles failed when comparing the harmonic current injection against the same standards.
Figure 1 – Example distortion data of a heat pump at each fundamental (top) and total resultant distortion (bottom)
“If we were to consider the worst performing, least compliant electric vehicles, there is a high probability that the total harmonic distortion would impact the distribution and electrical equipment more than the overall electrical load.”
As engineers we can control which heat pumps are installed and design systems to work with acceptable levels of distortion. When designing large electric vehicle charging infrastructure, not knowing the characteristics of the final loads you may be supplying makes designing the infrastructure much more difficult. If we were to consider the worst performing, least compliant electric vehicles, there is a high probability that the total harmonic distortion would impact the distribution and electrical equipment more than the overall electrical load.
Since the publication of Approved Document S, the number of electric vehicle charging points has increased exponentially. There are multiple sections within this building regulation that cover new and existing residential and non-residential sectors. The largest impact is to new residential schemes in which all dwellings must have access to an electric vehicle charging point (EVCP), thus with schemes in which there are a greater number of apartments to parking spaces, all spaces must have an EVCP.
The recent update (September 2022) to BS 7671 wiring regulations introduced the option to diversify the load of electric vehicle chargers provided that a load management system is incorporated to ensure that the building does not become overloaded. Active and dynamic load management systems are available as methods of controlling and limiting output on EVCPs. Active load management uses CT clamps on the main incoming cables and monitors the supply so as not to overload the main fuse. For example, a site could be set at 400A, and the CT clamp would monitor the landlord’s and tenants’ usage and alter the output of all EVCPs to an acceptable limit. Dynamic load management monitors the output of each EVCP so as not to overload a pre-set limit. For example, a group of EVCPs could be set at a maximum limit of 100A. These techniques can be used in conjunction, for example, the dynamic setpoint would limit the EVCPs to a pre-set limit but allow this to be exceeded when spare capacity was available on site without overloading the main fuse.
The electrification of transport and heat is predicted to cause a 30% increase in peak demand within local networks by 2030 (CIBSE, 2021). The strain on the National Grid is noticeable and causing delays due to an influx of large applications being registered recently. As such, the importance of a realistic load assessment that demonstrates the typical day-to-day electrical load has never been greater. At QODA there are several processes in place to better understand the impact of occupancy, heat demand, and load management on the electrical load of the building. Reducing the load and therefore minimising the impact on the grid is the key to improving the chance of a successful and punctual electrical utility connection quote.
“The electrification of transport and heat is predicted to cause a 30% increase in peak demand within local networks by 2030.” (CIBSE, 2021)
The Greater London Authority (GLA) has been working with the local distribution network operators (DNOs) UKPN and SSEN, to strategize the short, medium, and long-term solutions for the constrained grid. The current plan is to prioritise electrical infrastructure upgrades for affordable housing. SSEN and National Grid have also agreed to progress with developments that have an electrical demand below 1MVA (or that can be phased to require less than 1MVA per year) without long transmission infrastructure upgrade wait times.
Figure 2 – West London Electrical Capacity Mapping (SSEN, 2022)
There will likely be changes in the next few years which will impact and hopefully improve the relationship between the network and the community. The idea of a ‘prosumer’ (combined producer and consumer of electricity) is not new, however, it has recently been introduced (September 2022) into the latest BS 7671 wiring regulations. Electrical energy management systems (EEMSs), likely incorporated through another generation of smart meter, will be a key component of a prosumer’s electrical installation (PEI), allowing them to interact with a future smart grid and react to changes and spikes in local consumption. In the case of large projects, it may be feasible for local battery storage systems with on-site generation (e.g. solar PV) to be used in a PEI as a method of reducing demand on the grid and offering flexibility to the network when constrained.
Electric Vehicles will soon become a resource for which building and/or grid stability can be improved. Vehicle-to-grid (V2G) arrangements are being tested to determine how they can be best utilised and programmed. For example, does the optimum system prioritise building load stabilisation or grid export for peak demand reduction, and how the vehicle owner is therefore subsidised. Establishing the best method of calculating the State of Charge (SoC) of all connected EVs will play a significant role in estimating the useful output of the system. SoC is an estimation of the amount of charge within the battery cells as a percentage compared to the nominal capacity of the cells based on multiple calculations (voltage, coulomb counting, extended Kalman filter, and equivalent circuit models), commonly within a machine learning logic controller. This SoC calculated estimate must also take into account the user-set vehicle charging limits (e.g. 85% maximum charge), cell temperatures, losses, self-discharge rate, and deterioration of cells.
To make PEIs work, the earthing arrangement of the building must be considered in both ‘connected mode’ and ‘island mode’. In most situations, in ‘connected mode’, the DNOs earthing arrangement is used (TN-C-S). Upon disconnecting from the grid and switching to ‘island mode’, the live conductors must be disconnected, and a Neutral-Earth bond must be introduced to provide a TN-S arrangement. This must be factored into the electrical calculations to ensure the installation is compliant in both modes with both earthing arrangements.
Figure 3 – Earthing arrangements (IET, 2021)
In short, the success of an all-electric building lies in passive building design and considered but realistic demand reduction techniques.
CIBSE, 2021. TM67 – Electrification of buildings for net zero, London: CIBSE Publications.
CIBSE, 2023. Current thinking: connecting a large all-electric housing estate in West London. CIBSE Journal, January.
Greater London Authority, SSEN, 2022. West London Electrical Capacity Constraints, London: s.n.
IET, 2020. Code of Practice for Electrical Energy Storage Systems, London: s.n.
Written by Henry Metcalfe