Mixergy – Smart Hot Water Storage Tanks

Published: 3 August 2020

Mixergy has designed an innovative, smart hot water storage tank that allows consumers to heat only the water they need, in contrast to conventional hot water tanks which heat all or nothing. This saves on energy, cost and carbon emissions.

Energy Systems Catapult utilised our Home Energy Dynamics modelling toolkit (HED) to help Mixergy simulate how their hot water tank interacts with varied building and occupancy profiles without needing to deploy the innovation in the real world.

HED can be used to simulate the energy and carbon savings provided by low carbon heating solutions, either as standalone measures, or in combination with other energy efficiency measures.

The Innovations

 

Mixergy has designed an innovative, smart hot water storage tank that uses a controlled recycle flow through a diffuser to a heater at the top of the tank to produce a very sharp thermocline (boundary between hot and cold water) – so water at the top of the tank can be heated as required, rather than trying to heat the entire volume at once.

Being smart, the Mixergy tank learns how much hot water the householders use, so this top-up technology enables selective heating of water which improves the efficiency, reduces heat losses and moreover, it could allow for a smaller size tank thereby conserving space. The heating element at the top of the tank works together with a variable speed pump which operates when the hot water demand is above a certain level of the tanks total volume (e.g. 15%).

Mixergy tanks can provide hot water through direct electric heating (immersion heaters) or indirectly through an internal coil, which is designed to work with electric, gas or oil-fired boilers. Additionally, they can be fitted with external heat exchanger for use with heat pump systems.

 

Home Energy Dynamics is an innovative toolkit that analyses the interaction between different aspects of domestic heating, building fabric, hydraulic systems and consumer profiles to provide data and analysis on the efficiency and cost effectiveness of low carbon technologies for a whole range of UK housing types.

HED has been tested on a number of homes to date, to demonstrate a very strong correlation between predicted and measured energy performance, which supports validation work undertaken with Salford University’s Energy House.

Our Approach

To match the profile of a home being used by Mixergy in a real-world trial, a semi-detached three-bedroom 2-story house (steel framed modular-build) was selected for the HED simulation from a library of existing housing types compiled by the HED tool-kit. The house has three bedrooms on the first floor with a bathroom and landing. The ground floor is open plan including a dining room, kitchen and a living room. It is assumed that the hot water storage tank is in the utility room on the ground floor.

The HED model ran a two-week simulation comparing the performance of a Mixergy hot water storage tank with a conventional storage tank to establish the difference in energy consumption between both systems.

Occupancy profile

The HED model is novel in its inclusion of occupancy data from a range of different households, rather than relying on standardised occupancy patterns. This is continually refined by insights from our Living Lab – the Catapult’s unique real-world trial facility of 100 connected homes, where innovative businesses can rapidly design, market-test and launch smart energy products and services.

Hot water consumption patterns can vary significantly between different homes according to the size and behaviour of the household. In order to address different hot water usage patterns, we selected two consumption profiles from a range of possible options:

 

Family of five

The first occupancy profile comprises an adult couple with two teenagers and a pre-school child, one of the parents working part time and the other working full time.

 

Family of two

The second occupancy profile comprises a retired couple.

The household profiles contain data about the desired temperatures and heating schedules for each room in the house, occupancy and appliance heat gains, openings of doors and windows and the hot water consumption details for occupants.

Heating systems

The house modelled by HED is assumed to have a fully electric heating system, so the direct electric hot water option was chosen to evaluate:

  • Fully electric heating: The home heating system comprises electric panels for space heating (SH) demand and a hot water storage tank with direct electric heating. Both the conventional and Mixergy storage tanks were modelled with immersion heaters (max 3 kW).
  • The target temperature for the two hot water storage tanks being compared in the simulation is set to 55C and to reduce the risk of legionella’s disease/infection, heating to 65C is included once a week for both Mixergy and conventional storage tanks.

The Outcomes

HED simulated the total energy input into each hot water tank in kWh and the the actual energy extracted from the tank in the form of hot water. Cumulative electricity consumption and carbon emissions also includes the energy from space heating for the two week period.

In both cases, the results illustrated that the Mixergy tank operates more efficiently compared to the conventional storage tank. The reduction in energy consumed (KWh) by the Mixergy cylinder v conventional.

  1. Family scenario = (116.1 v 129.2) ~11% reduction
  2. Couple scenario = (56 v 65.1) ~14% reduction

The inputs and outputs of energy for the Mixergy tank were very close which implies the Mixergy tank loses less energy in comparison to a conventional tank.

Since the completion of the project, a real world Mixergy trial of 66 units in Cornwall, was found to deliver a 12% reduction energy consumption. An outcome very similar to the HED identified savings of between 11-14%.

NOTE: It is worth highlighting that the HED simulation performed in this study did not take into account Mixergy’s Machine Learning schedule optimisation function that could potentially lower energy and carbon even further by factoring in off-peak vs. peak tariffs.

The Impact

Modelling the performance of the Mixergy smart hot water tank demonstrated both the ability of the innovation to save consumers energy, cost and carbon emissions, and the accuracy of the Home Energy Dynamics (HED) toolkit and its ability to quickly and accurately identify the effectiveness of a low carbon solution.

HED can provide innovators with detailed performance data and analysis of new heating technologies and low carbon solutions, in combination with building fabric upgrade options and different occupancy profiles, which can provide evidence for product and service offerings for both developers of new housing and the growing home retrofit market.

“Working with Energy Systems Catapult and their Home Energy Dynamics modelling toolkit has been a really insightful process. It allowed us to test Mixergy’s product when deployed in a varied ecosystem of products and applications, which is often challenging to model. These insights are extremely valuable when articulating to prospective clients and stakeholders the full impact of deploying smart home technologies.

“We were really impressed with the accuracy of the model and also how it is able to quickly identify effectiveness of a solution without need for a full laboratory set-up.”

David White, Head of Commercial Operations, Mixergy

“We are delighted to apply our dynamic modelling toolkit to help Mixergy on their exciting journey, and to continue enhancing our library of innovative low carbon heating solutions which builds on our experience on the Smart Systems and Heat programme, Electrification of Heat project, our 100-home Living Lab and our Innovator Support Platform.”

Bunmi Adefajo, Modelling Business Lead, Energy Systems Catapult