Hot Water Storage Systems (Thermal Stores)

Thermal Stores & Hot‑Water Storage Systems

Here at Gondwana, we have been designing, installing and supplying unique, high‑spec thermal stores for over fifteen years—serving the public, the trade and our own renewable‑heating projects.

Hot‑water storage systems—also known as accumulator tanks, buffer tanks or thermal stores—sit at the heart of Gondwana Green Heat’s work. You simply cannot make full use of the heat generated by solar thermal, wood heating or heat pumps without a correctly sized, high‑quality storage system.

We design, import, supply and install tanks from 35 litres to 200,000 litres for the UK market—covering everything from a wee shepherd’s hut to large industrial buildings and district‑heating applications. Whatever the scale, the principle is the same: stable heat storage, efficient system control and long‑term reliability.

If you need help with a project, please don’t hesitate to get in touch.

Thermal Stores, Buffer Tanks and Accumulator Tanks

Thermal Store System Design

A well‑designed thermal store is the central hub of a modern multi‑source heating system. Its job is simple: capture heat efficiently, store it safely, and deliver it reliably. But achieving that requires careful engineering, correct sizing, and the right internal configuration.

Below is a full breakdown of how thermal‑store system design works and the principles we apply at Gondwana.

🔧 Core Design Principles

1. Heat Input Strategy

A thermal store can accept heat from almost any source. System design begins by identifying which inputs you need:

• Gas boiler
• Oil boiler
• Log gasification boiler
• Pellet boiler
• Wood‑burning boiler stove
• Solar thermal
• Solar PV immersion
• Heat pump

Each heat source has different flow temperatures, output profiles and control requirements. The thermal store must be configured so every source can contribute efficiently without interfering with the others.

🌀 2. Internal Coil & Exchanger Configuration

Inside the store, we specify the correct combination of:

• Solar coils
• Boiler‑stove coils
• Heat‑pump coils
• DHW coils
• Plate heat exchangers
• High‑temperature and low‑temperature zones

The layout is critical. For example:

• Solar coils must sit low in the tank to harvest cooler water.
• Boiler‑stove coils sit high to capture high‑temperature combustion heat.
• Heat pumps require large surface‑area coils for low‑temperature efficiency.
• DHW can be delivered via internal coils or external plates, depending on flow rate and hygiene requirements.

Correct coil placement ensures stratification—hot water at the top, cooler water at the bottom—which is essential for system performance.

📏 3. Correct Tank Sizing

Tank volume is determined by:

• Heat‑source output
• Number of heat sources
• Domestic hot‑water demand
• Space‑heating load
• Building type (shepherd’s hut vs industrial building)
• Desired autonomy (how long the store should hold usable heat)

Gondwana supplies stores from 35 litres to 200,000 litres, allowing us to design systems for everything from tiny off‑grid cabins to large commercial buildings and district‑heating networks.

🔥 4. Multi‑Source Integration

Thermal stores excel when combining multiple heat sources. For example:

A home with an oil boiler, solar thermal, and a boiler stove can run all three into one store. The store becomes the central “thermal battery”, absorbing heat from each source and distributing it as required.

This approach:

• Removes the need for a separate vented/unvented cylinder
• Simplifies pipework
• Improves system efficiency
• Reduces maintenance
• Future‑proofs the property for additional heat sources later

🚿 5. Domestic Hot Water Delivery

We offer two main DHW options:

• DHW coil inside the store
• External plate heat exchanger

Plates are ideal for high‑flow properties or commercial sites. Coils are perfect for domestic systems where simplicity and reliability are key.

Both options eliminate the need for a traditional hot‑water cylinder.

⚙️ 6. Controls & System Logic

A thermal store is only as good as its control strategy. We design systems so each heat source:

• Fires at the correct time
• Prioritises efficiently
• Avoids conflict with other sources
• Protects the store from overheating
• Maximises stratification
• Delivers stable DHW temperatures

Our control platforms ensure the system behaves predictably and efficiently, regardless of how many heat sources are connected.

🏡 7. Application Examples

Thermal stores are ideal for:

• Multi‑source homes
• Rural properties
• Off‑grid buildings
• District‑heating networks
• Biomass systems
• Solar‑thermal installations
• Heat‑pump integration
• Boiler‑stove heating
• Commercial and industrial sites

From a wee shepherd’s hut to a 200,000‑litre industrial accumulator, the design principles remain the same.

a small 300 litre, high spec thermal store for oil, solar thermal and a boiler stover, getting winched into a loft.

GONDWANA THERMAL STORE PRODUCT RANGES

We supply two main product ranges:

🛢️ Off‑the‑Shelf Thermal Stores

We supply UK and European‑manufactured tanks in:

• Copper
• Stainless steel
• Carbon steel

These tanks offer:

• Cost‑effective solutions
• Versatile configurations
• Hundreds of size, shape and coil options
• Reliable performance for domestic and commercial systems

Ideal for standard installations where conventional sizing and coil arrangements are suitable.

🧱 Custom Thermal Stores

Gondwana is best known for our custom hot‑water storage solutions. These can be manufactured in copper, stainless steel, carbon steel or hybrid combinations.

Benefits of custom tanks:

Shapes

• Tall and slim
• Squat
• Oval
• Rectangular
• Cube tanks

Insulation

• Factory‑fitted jackets
• Detachable on‑site insulation
• Foam‑filled on‑site options
• Thickness from 50 mm to 300 mm

Pressure Options

• Vented
• Pressurised
• Hybrid systems via heat exchangers

Heat Exchangers

• Extra‑long coils for maximum heat transfer
• Solar thermal coils
• Heat‑pump coils
• DHW coils
• Section‑separating coils for multi‑zone systems

Electrical Inputs

• Immersion heaters for PV/turbine input
• Direct‑electric DHW
• Direct‑electric wet heating

Specialist Heat‑Pump Stores

• Massive 32‑metre, ¾‑inch finned copper DHW coils
• Larger options available

Custom stores allow complete freedom to design exactly what the project requires — no compromise on shape, size, coil layout or insulation.

APPLICATIONS

Thermal stores are ideal for:

• Multi‑source homes
• Rural properties
• Off‑grid buildings
• District‑heating networks
• Biomass systems
• Solar‑thermal installations
• Heat‑pump integration
• Boiler‑stove heating
• Commercial and industrial sites

From a shepherd’s hut to a 200,000‑litre industrial accumulator, the design principles remain the same.

NEED HELP WITH A PROJECT?

We design, import, supply and install thermal stores across the UK. If you need help with a project — domestic, commercial or industrial — please get in touch.

Components & System Accessories

Alongside our thermal storage tanks, Gondwana Green Heat supplies a comprehensive range of components designed to complement, enhance and control your heating system. These accessories ensure correct operation, maximum efficiency and long‑term reliability across all heat sources.

⚙️ Differential Temperature Controllers (DTC Controllers)

DTC controllers are used to manage and optimise heat generators such as:

• Gas boilers
• Oil boilers
• Solar thermal systems
• Heat pumps
• Wood‑burning boiler stoves (pump control)

They monitor temperature differences across the system and activate pumps or valves at precisely the right moment, ensuring efficient heat transfer and protecting equipment from overheating or poor circulation.

🔥 Loading Valves (With or Without Pump Groups)

Loading valves ensure correct return‑temperature protection for biomass boilers and boiler stoves. They:

• Maintain ideal combustion temperatures
• Prevent condensation damage
• Improve boiler efficiency
• Extend boiler lifespan

Available with integrated pump groups or as standalone valves depending on system design.

🧱 Additional Insulation Options

Correct insulation is essential for thermal‑store performance. We offer:

• Extra insulation jackets
• Detachable on‑site insulation
• Injection foam insulation (applied on‑site)
• Thickness options from 50 mm to 300 mm

These upgrades significantly reduce heat loss and improve overall system efficiency.

🚿 Stainless Steel Plate Heat Exchangers (45 kW – 2000 kW)

We supply high‑quality stainless‑steel plate heat exchangers for:

• Domestic hot‑water production
• Separating system zones
• Linking vented and pressurised circuits
• High‑flow commercial DHW applications

Available from 45 kW to 2000 kW, these exchangers are commonly paired with our thermal stores to deliver powerful, hygienic and efficient DHW performance.