Page 36 - Plumbheat Magazine

Solar
Solid Gas Fuel or Oil
Wood Burners & Thermal Stoves
Thermal Stores and Wood Burning Stoves – What You Need to Know
Wood burning stoves are an increasingly popular feature for home-owners and while some opt for a decorative heating appliance, many are looking to use the heat generated to also provide hot water.
USING UNVENTED cylinders is generally not allowed due to the uncontrollable heat generated by the stove. There are certain stoves on the market capable of linking
to a pressurised system but they have multiple levels of safety control which can be very complicated.
The optimum hot water storage solution for wood burning stoves, are therefore thermal stores, thanks to their unique ability to deliver mains pressure hot water, while keeping the rest of the system open vented.
The Basic Principles of a Thermal Store
The thermal store reverses the traditional approach to hot water, where the stored water goes to the taps. Instead a thermal store is heated, to generally a higher temperature and the store of water can be circulated round the Central Heating circuit.
Additionally - mains pressure secondary
water is passed through a high efficiency coil
or external plate heat exchanger and draws its heat from the store, before going through
a thermostatic mixing valve, blending it
to the required tap temperature.
The stored water is primarily heated by the solid fuel appliance, while a traditional boiler, solar thermal
or PV, or an electric immersion can be used for additional heat. Thermal stores are recognised as the most flexible hot water storage solution for
incorporating multiple energy sources, including renewables.
Integrating a Wood Burning Stove
To enable the heat generated by the wood burning stove to be transferred to the thermal store requires the use of an integrated back boiler which is connected via a minimum of 28mm Flow and Returns.
To allow gravitational forces to take effect and start the cycle of heat flowing round the system there must be a minimum of 500mm between the centre
of the F & R connections on the wood burning stove and the thermal store F & R. The more height between these connections, the quicker the stored water will heat up.
How Do You Prevent Over Heating?
A thermal store will generally sit at around 75-85oC however when the wood burning stove is used regularly, the heat generated needs to be controlled.
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This is achieved by installing an overheat stat linked to the central heating pump which is activated when the stored water reaches in excess of 85oC, dissipating the heat through the heating circuit.
A “quench coil” maybe also be advisable where power cuts are likely, allowing cold mains to pass through a small coil in the thermal store which in turn cools it down.
McDonald Engineers UK can also fit a Pressure & Temperature Relief Valve to the store.
Why a Thermal Store
Ideal for solid fuel and multiple heat sources, reduced installation requirements, no unvented discharge rules, very limited servicing requirements., zero legionella risk and drinkable hot water at all hot taps.
McDonald Engineers UK have the widest range of thermal stores – including their rectangular CUBEflow unit.
As well as providing full technical
advice on any aspect of hot water storage solutions, McDonald Engineers UK can also customise connection layouts to simplify the installation process.
For more information visit www.mcdonald-engineers.com or call on 01592 611123 •