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What is a thermal heat store?

Thermal heat stores explained

It might sound like a power-up from a grainy PS One shoot-em-up. But a thermal heat store is one of the fastest growing renewable heating technologies around as a means for holding excess heat.

Thermal heat stores can be used with a single renewable heating technology or to mix different renewable heating technologies together. They can also be utilized alongside your typical boiler or immersion heater.

There’s no doubting that for the time being, thermal heat stores are a lot more popular within commercial ventures as opposed to residential properties. They are known to perform especially positively alongside heat pumps, biomass boilers, and both wind and solar heating systems.

You might be a lot more accustomed to designer radiators and towel rails with regards to your basic home central heating.

But if you are keen to go green, thermal heat stores are well worth looking into.

So, what is a thermal heat store and how does it work?

House behind trees featuring black solar panels on a red tiled roof

What does a thermal heat store do?

Ok, so you might not use 50 toilet rolls at once. But they’re always handy to have in at a time of need. You can apply a similar logic to the way a thermal heat store works. They essentially hold and manage renewable heat until it is required.

In residential spaces, heated water will typically be contained within a big, insulated cylinder tank. They’re commonly known as accumulator tanks or buffers.

Thermal stores will also likely feature a single or multiple heat exchangers – external flat plates or internal coiled pipes are the usual suspects. An electric heating element might also feature, like an immersion heater.

All sorts of technologies can contribute to a thermal heat store, as long as it has been designed to work with them. Heat pumps, solar water heating and wood-fuelled boilers are heating source examples a thermal heat store can take from.

Now, what do thermal heat stores have to offer?

Close up of left hand adjusting dials on a central heating boiler

Advanced emerging heat storage technologies

There are a number of thermal energy storage technologies, beyond traditional water tanks, that can provide increased storage density and efficiency. We have listed some of these emerging technologies as follows…

Phase Change Materials (PCMs)

PCMs store energy via the use of a reversible phase transition, such as melting and solidifying. This enables them to hold a large amount of heat with only a slight temperature variation, resulting in between five to 10 times higher storage density in comparison to sensible heat storage in water. However, PCMs often incorporate low levels of thermal conductivity, and thus require effective heat transfer solutions.

Thermochemical storage

Thermochemical storage utilises reversible chemical reactions so that sizeable quantities of heat can be stored in a compact volume. When the application of heat occurs, the material is broken down into separate components which are then able to be stored. Once the components are recombined, the stored heat is released. At the time of writing, this technology remains in the research and prototype stage.

Solid-state storage

Solid-state thermal energy storage technologies, for instance, those using concrete or alternate solid materials, are another form of emerging potential substitutes to water tanks. These can deliver a higher storage density and provide reduced heat loss measured against liquid-based systems.

What can a thermal heat store provide?

  • Hot water only (typical of a solar water heating system)
  • Space heating only (typical of a heat pump system)
  • Both mains pressure hot water and space heating

To get the very best out of a thermal heat store, it can be tasked to control several heat outputs and inputs. For instance, excess solar heat could be utilized for space heating, or to pre-heat a heat pump before it delivers hot water.

White central heating boiler with dial and digital display on blue background

Advantages of a thermal heat store

  • Thermal heat stores allow warm water to be heated by an extra heat source like an electric immersion heater or a standard boiler.
  • Enables the use of a wood burning boiler stove at optimal efficiency without causing the room to overheat.
  • Allows renewables heating systems to operate more efficiently. This point is especially prevalent in relation to wood-fuelled heating systems like log boilers. These types can perform at a high efficiency – greater than when kept ticking over – when put to work at maximum output.
  • Eliminate the requirement to purchase expensive fossil fuels to cope with the pressure of on-demand space heating or hot water.
  • Facilitates the storing and managing of renewable energy resources, accounting for the difference in time from heat being available to being required. For instance, users could be storing water heated by a solar thermal heating system within the day, ready for use at a later time when none or limited solar energy is accessible.

Different types of thermal heat stores

There are several types of thermal heat stores available, each designed to flourish in accompaniment with various renewable technologies. Below is an overview of some of the main types of thermal storage solutions on the market…

Heating engineer with red gloves attaching outer shell of boiler onto boiler system

Thermal heat stores for heat pumps

Heat pumps, of both the ground source and air source variety, will operate more efficiently when there is less wear on the compressor and pump. Thermal heat stores will ensure that your pump won’t have to constantly cycle on and off when there’s a low heat demand, preserving the pumps for a better performance.

The thermal stores most commonly used in conjunction with the likes of air source heat pumps are buffer tanks. There are other means, like leaving a part of the heating system open permanently.

In line with manufacturer recommendations, your installer should guide on whether a buffer tank is a suitable option to team with your heat pump. And, if so, what size buffer tank is appropriate for an effective heating circuit.

Thermal heat stores for solar water heating

Thermal heat stores are an especially good option in cohesion with solar water heating systems, considering they can utilise solar thermal energy for both space heating and the heating of water.

On a warm summer’s day, you might find that a solar thermal heat store will take stock of plenty more energy than necessary to run just a hot water tap. And with space heating also covered, you can quite literally make hay while the sun shines with a thermal storage system that operates with such energy efficiency.

There’s also the opportunity to prioritise solar thermal energy above any other heat source. Settings can be adjusted so that if no solar heat can be generated, no other heat source will be tapped in replacement.

Close up of Vaillant boiler with digital display and multiple dials

Thermal heat stores for biomass heating systems

Biomass heating systems, or wood-fuelled heating systems, are the types most commonly associated with thermal heat stores.

And for good reason too – thermal storage is crucial to the efficiency of biomass boilers and heating resources of that nature. Especially log boilers, which by design burn an array of logs at high efficiency as opposed to small totals over a longer period of time. Log boilers linked to large thermal stores are used in this manner.

Also, thermal heat stores can bridge the gap between the time it takes to ignite the boiler or stove and the hot water demand. It does this by storing and managing hot water preserved from the last time the boiler or stove was lit.

Thermal heat stores used for biomass boilers or other wood-fuelled heating systems are typically quite big. That is due to their propensity to provide space heating in addition to hot water. The buffer tanks or accumulators will usually have the capacity to store between 500 and 5000 litres of water. They can retain the hot water for multiple days if they are insulated properly.

But that isn’t to say that smaller thermal heat stores aren’t effective alongside stoves with back boilers and boiler stoves. Thermal storage tanks with a capacity of up to 300 litres are appropriate options for the likes of stoves that feature in living areas, being fed by fuel over the course of the day.

There’s a difference in the level of heat that boiler stoves and stoves with back boilers emit into the room or turn to water. Stoves with back boilers will typically only covert around 20 per cent of their output into water. With boiler stoves, the water conversion rate is closer to the 65 per cent mark.

Plenty of factors will contribute towards deciding the size of thermal heat store required for a biomass heating system. Especially so, which type of wood is being used for renewables heating energy.

For instance, a log boiler would require a large thermal store for reasons already outlined earlier in the piece. Pellet boilers, by contrast, would only need relatively small thermal storage as they can adapt to rapid heat demand fluctuations.

Your system installer could probably advise on what size thermal heat store you need to get the best overall performance from your renewable heating system.

Renewable heating combinations

A variety of renewable heating systems can be combined via the use of thermal storage. A solar water heating system can be teamed with a wood burning boiler stove, for instance.

Other examples of thermal heat store connectables follow…

  • Conventional boilers
  • Electric heating elements like immersion heaters
  • Single or multiple renewable energy technologies (biomass, solar, heat pump)

Frequently Asked Questions

Thermal heat stores can provide either solely hot water, usually in cohesion with a solar water heating system, or only space heating, typically alongside a heat pump system. Finally, thermal heat stores can provide a combination of mains pressure hot water and space heating.

That said, thermal heat stores can work alongside renewable energy solutions or boilers to deliver the appropriate heating devices within a property, such as designer radiators or heated towel rails.

For further information, browse our dedicated blog, What is a thermal heat store?

In the main, thermal heat stores are used for commercial premises, where it is imperative that there are always reserves of heat or thermal energy on hand. A thermal heat store holds onto excess heat with the use of a single or multiple renewable heating technologies, so a thermal energy deficit is never a concern.

Thermal heat stores perform especially well alongside ground and air source heat pumps, as well as solar panel systems and biomass boilers, which are also currently more commonplace with regards to commercial ventures as opposed to residential properties.

Explore our blog, What is a thermal heat store?, for further details.

A thermal heat store is a form of renewable heating technology that is used for the storage of excess heat. They can be used alongside a sole renewable heating system or a combination of renewable technologies, and can also be utilised in cohesion with a standard boiler or immersion heater.

Essentially, thermal heat stores hold on to surplus renewable heat until it is required, so properties never find themselves short of necessary power at a time of need. This is one of the reasons thermal heat stores are a popular commercial solution, with residential spaces tending to rely on more traditional heating devices such as designer radiators drawing from boilers and the like.

To find out more, take a look at our dedicated blog, What is a thermal heat store?

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For more information about any home heating solutions, don’t hesitate to get in touch with us at BestHeating. You can leave your queries or thoughts in the comments section below, or contact us via FacebookInstagram or Twitter.

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