Water heating for net-zero: what installers need to know – Heating, Ventilating & Plumbing

Pete Armstrong, CEO of Mixergy, says that, as we move towards net-zero, it is crucial that the newest renewables-connected water storage systems remain fast, convenient, and cost-effective for end-users.

The way we heat water in our homes is changing at an increasing pace, and with looming net-zero targets, a fabric-first approach to designing heating systems is growing in importance. However, even though our hot water energy consumption is likely to increase, householders still need fast and convenient hot water that does not become a greater burden on their already volatile energy bills.

As we make the move from heating our homes with gas to electricity, whether we are installing a heat pump, solar panels, or electric storage heaters, the only way of achieving quick-filling baths or running a typical power shower within the capacity of the electrical grid is through storing hot water.

A typical gas supply can easily deliver 30kW of instantaneous power to a combi boiler for the production of on-demand hot water. A typical electricity supply, by comparison, can only deliver a maximum of 18kW, meaning it struggles to deliver the instant power needed for a high flow rate shower, alongside all the other competing demands in the home.

Consider that the future demands on our mains connections also include EV chargers (7.5kW). For this reason, we need to produce hot water more gradually in hot water tanks whichever way we go about it (direct electric or heat pump).

So, when replacing a system or heat-only boiler, where theres already a cylinder in place, its important to engage in a conversation with the homeowner about futureproofing their heating system. For example, the Mixergy smart cylinder has received validation from the Energy Saving Trust for being up to 21% more efficient than traditional cylinders when operating with a standard gas system boiler, while at the same time being heat pump and solar-ready.

This proactive approach allows homeowners to make choices that can contribute to significant cost savings today, while being prepared for either a heat pump or solar panel installation in the future, thanks to easily installed retrofit solutions.

Flexible tariffs

Flexible electricity tariffs are becoming more available as the rollout of the latest generation of smart meters is completed. Second generation smart meters allow energy suppliers to operate real-time dynamic pricing, which means that whenever the wind blows, lower cost electricity can be passed through to the householder.

Were all familiar with Economy 7 tariffs where the cost plummets for seven hours at night, however we are now entering into a world of Economy 24/7, which means the energy supplier can turn on your hot water whenever excess electricity is being generated.

Traditional Economy 7 cylinders would have two heating elements; a bottom heating element connected to the off-peak supply, and a top element connected to a permanently live feed to allow for a quick boost. Tariffs will become much more flexible and this flexibility is core to what Mixergy is about.

Thermal stratification

Exploiting thermal stratification is one way we can make our hot water storage more energy efficient. Simply put, thermal stratification is the result of heat rising; hot air rises above cooler air and hot water floats on top of cooler water.

Most hot water cylinders work by heating the water using coils or a thermostat at the bottom of the cylinder, and then heating all the water in it, like a big kettle, irrespective of how much hot water is actually needed.

The Mixergy cylinder starts by heating a small volume of water at the top of the cylinder and then growing that volume downwards. The Mixergy cylinder therefore behaves a bit like a traditional Economy 7 tariff, but one with an infinite number of heating elements, meaning the user as much control as they like on how much or how little to heat.

Using thermal stratification and smart technology, the tank only heats the water needed, reducing heat losses. And the water gets to a useful temperature quicker. In addition to saving energy, only heating the water needed leaves more space to accommodate surplus solar energy for properties equipped with solar panels, or exploit low cost energy for those on a flexible electricity tariff.

The value of heating engineers

Good heating engineering, refurbishment, and building demands a high level of technical skill. This is true whether were talking system specification from heat loss calculations, making good after upgrading pipework, or making sure that controls operate together seamlessly.

In the UK, we should really consider our tradespeople as craftspeople, as they do in other parts of Europe.

I think we need to break down the delineation between the trades, particularly electrical and plumbing. The idea you need a plumber for pipework and an electrician for wires is prohibitive when installing new technologies.

The first thing I would recommend is that heating engineers get their Part P and 18th Edition Wiring qualifications. Without these, it becomes very difficult to do a heat pump installation with multi-room TRVs, thermostats, and smart technology. For a qualified gas engineer, it isnt a big step to qualify to do electrics.

Having additional skills alongside the core plumbing and heating tickets around MCS, Unvented G3, Gas Safe, and so on, will give heating engineers much more flexibility to deal with a wide range of projects.

Theres a shortage of heating engineers in general and a growing need for renewable installers. We need to find a way to encourage more into the sector. Keeping people warm while helping bring the transition to net-zero is a highly rewarding, appreciated, and sought-after skillset.

In conclusion, I hope that if you are a heating engineer who is reading this, you fully appreciate the value of your skills at this crucial time and that you might consider talking to your customers about the role that smart cylinders can play in getting the best from your gas boiler while being renewable ready, whether thats with a PV installation, a heat pump, or simply flexible tariffs.

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Water heating for net-zero: what installers need to know - Heating, Ventilating & Plumbing