Heatbank Xcel Installation and User Instructions

This page is currently a Work In Progress. May 2018.

This page is intended to form a repository of information intended to form a kernel of content that will ultimately lead to an up to date set of Installation and User Instructions for the Xcel.

Installation Instructions

Installation Instructions for the HEATBANK Xcel Comprehensive installation manual for the HEATBANK Xcel thermal Store.

Introduction

Congratulations on your purchase of the Xcel Heat Bank® Thermal Store. The Xcel is manufactured in the UK from high quality Duplex stainless steel offering exceptional strength and corrosion resistance, back up by a lifetime guarantee. The insulation levels of the cylinder meet the requirements of Building Regulations Part L.

The Xcel store is intended to permit a variety of different heat sources to contribute towards the provision of domestic hot water (DHW) and central heating in your property. The store is not a heating appliance in its own right and is reliant on the appliances that are connected to it to deliver the energy required to support your hot water and heating requirements. It is therefore important that those heating appliances are correctly rated for the size and configuration of the Xcel store they will connect to, and for the heating and hot water demands of the property it is installed in.

The Xcel store is manufactured in a number of different variants and your unit will be supplied in a specification matching those requirements given to Thermal Integration by the purchaser at the time the unit was ordered. The following set of installation and user instructions are tailored towards that specification. If your system has a different specification, or you require information on other variants available, please contact Thermal Integration Ltd. (Tel: 0345 2411441).

Overview / Principle of Operation

The Xcel thermal store permits the connection of two or more heat sources together into one system, to collect primary heated water that can be delivered to central heating circuits – radiators and/or underfloor heating (UFH) - or can be utilised to create domestic hot water (DHW). These heat sources can either be conventional, fossil fuelled boilers (oil, gas, LPG) or renewable sources (wood burning boiler stoves, biomass boilers, solar thermal panels). Furthermore, electric immersion heaters can be installed that allow back up or secondary heat input from either the mains electricity supply or solar PV (if installed).

By combining the heat from these different sources into one store, it not only permits sources such as solar to contribute to central heating as well as hot water, but the cylinder itself acts a buffer, (where solar is connected) collecting and storing energy captured during the daytime when there is little or no demand, and allowing it to be utilised in the evening when this source has diminished or disappeared. The physical structure of the cylinder also acts as a ‘neutral point’ in the overall system – in other words it permits different appliances to be interconnected and operate simultaneously without each one impacting on the other due to circulation forces from pumps, thermos-syphoning, etc. Another feature, if a wood burning stove is linked with an oil/gas boiler, is that the store controls permit the wood burner to deliver the maximum input it can to the store (dependent on rating of stove and frequency of refuelling) and thus respond to hot water/heating load, but with the oil/gas boiler providing a supporting or back up role. This enables the most to be obtained from the renewable heat source whilst minimising the reliance on fossil fuel.

It is important to understand that whilst the cylinder contains heated water, it is actually ‘Primary hot water’, that is, it is the water that passes through the heat exchanger of the oil/gas boiler, or the back boiler of a wood burning or biomass boiler. This same water is also what passes through radiators and/or underfloor heating loops. The cylinder does not, therefore contain Domestic Hot Water (DHW). Whenever a hot tap is opened, DHW is created ‘on demand’, at the moment it is required. This is done by passing the heated water from the store through one side of a plate heat exchanger, which heats up cold water from the mains passing through the other side of the plate. A very similar process takes place in a ‘Combi’ boiler. The reason for using a plate is the far superior performance this gives over a coil – both in duration and total DHW quantity delivered before the store becomes depleted. A more detailed analysis of the advantages are discussed Here:

The thermal store acts like a large vertical column of water, where the hottest water will naturally rise to the top of the store, and the coolest will fall to the base. This temperature gradient, or stratification, is an important feature of its operation. The higher temperature heat sources (gas/oil/wood/solid fuel) are delivered to the top of the store, with higher temperature demands (DHW, radiators) also drawn out of this upper region. Inputs from intermittent and variable sources like solar thermal are delivered to the coolest section at the store base to maximise low temperature gains; UFH which operates cooler than radiators also draws off lower down the store. The store is intended to operate ideally in the region of 70° to 75°C – that is, whilst on demand, the upper to mid region of the store should be heated to these temperatures for the best performance from DHW and for central heating by radiator. Higher temperatures are possible, for example from solid fuel or wood burning stoves, or possibly from solar thermal (depending on the set up of the solar controller, and weather conditions. The maximum operating temperature is 90°C: Temperatures in excess of this will cause the safety controls to start operating to reduce the stores temperature.

Heat sources are delivered to the top or upper part of the store and cooler water drawn from lower down. This enables a ‘top-down’ heating process that assists in maintaining stratification. Apart from solar thermal input, which is via a coil in the base of the store, heat sources are by default and preference connected directly to the store. Not only does this permit top down heating, it also allows the full output of the heat source to be delivered directly into the top of the store. Excepting solar, heat exchanger coils are not used in Xcel cylinders except where no other alternative is suitable. This is because their heat transfer capacity is often less than the output of the heat source, but also because they deliver diffuse heat to a region in the lower and mid sections of the cylinder which then convects to the top. The result is that heat up/recovery times are slower and depletion occurs more quickly than with direct systems. For example: Consider an Xcel store with direct boiler input versus a conventional hot water cylinder with boiler coil. From cold, the hot water cylinder may take at least 20 – 30 minutes before the tank is warm enough to deliver useable DHW. With the Xcel it may require less than 5 minutes before there is hot water available for basins and sinks.

The default mode of system installation and operation for the store is conventional, open vented. This permits the direct connection of most wood burning and solid fuel stoves and avoids the necessity to install discharge pipework for temperature/expansion relief safety valve, but still enables mains pressure DHW to be supplied. Furthermore this removes the need for installation and commissioning by a registered Unvented installer or for subsequent annual inspection and maintenance visits. If installation on a Sealed System configuration is however required, the appropriate controls and safety devices can be supplied pre-installed on the cylinder.

Unit Variants / Options

The Xcel thermal store is available in a number of options, covering a range of different heat source combinations and configurations. The standard options, referred to as Data Sheets are listed below – the options specify only the intended heat inputs. Unless specified, all stores are supplied fitted with a plate heat exchanger for the generation of DHW. Note that each option can be further altered or added to, to produce a bespoke product to better match the specifics of your system requirements:

• DS-1 Biomass boiler/stove Buffer Store (no DHW assembly)
• DS-2 Biomass boiler/stove Thermal Store – DHW via coil in tank
• DS-3 Biomass boiler/stove Thermal Store
• DS-4 Biomass boiler/stove + Gravity Wood Burner + Solar Thermal
• DS-5 Biomass boiler/stove + Solar Thermal
• DS-6 Gas/Oil fired boiler + Gravity Wood Burner + Solar Thermal
• DS-7 Gravity Wood Burner
• DS-8 Gravity Wood Burner + Solar Thermal
• DS-9 Biomass boiler/stove + Gravity Wood Burner
• DS-10 Gas/Oil fired boiler + Solar Thermal
• DS-11 Gas/Oil fired boiler + Gravity Wood Burner
• DS-12 Biomass boiler/stove + Solar Thermal – DHW via coil in tank
• DS-13 Biomass boiler/stove + Pumped Wood Burner + Solar Thermal
• DS-14 Gas/Oil fired boiler + Pumped Wood Burner + Solar Thermal
• DS-15 Pumped Wood Burner
• DS-16 Pumped Wood Burner + Solar Thermal
• DS-17 Biomass boiler/stove + Pumped Wood Burner
• DS-18 Gas/Oil fired boiler + Pumped Wood Burner
• DS-23 Gas/Oil fired boiler (Sealed System) + Pumped Wood Burner + Solar Thermal

Principles of Operation

As discussed earlier, the Xcel store is designed to establish and maintain a temperature gradient, or stratification, from the top to the bottom of the store so that heat from various sources is delivered to the upper part of the store where it can be then drawn out of and delivered to its destination, whilst cooler water for reheating, or returning from the target, is drawn from / delivered to the lower part. Thus in the heating phase, the store is heated from the top down, whist on demand, heat is draw from the top and cooler return water is delivered from the bottom up. A boundary region between these hotter & cooler layers is established and in normal operation this layer moves up and down within the store as heating capacity versus demand varies.

Heat Inputs

For those heat sources that are directly connected to the store, and are on pumped circulation, connection of the heat input – or Flow – is made at or very close to, the top of the cylinder. These sources include: Biomass boilers & stoves; Oil/Gas/LPG fired boilers; Wood burning or Solid Fuel boiler stoves on fully pumped or pump assisted connection. In all these cases it is intended that the temperature of primary water flowing into the store is controlled by a mixing valve (either pre-installed or required as part of the installation work), which ensures that the water entering the top of the store is at a minimum of 55° to 60°C. Cooler water going back to the appliance for reheating - or Return - is draw off the bottom of the store. Thus, in a heating only phase (i.e. no demand placed on store), primary heat is pumped into the top of the store and the body of heated water travels down the store, pushing the hooter/cooler boundary region down, until the store is fully heated from top to bottom.

• Note: Where a solar thermal coil is fitted at the base of the store, the Return connection is made just above the top of the coil. This allows for a ‘Solar Reserve’ at the base of the store, in the region that this coil sits in, that remains relatively cool in relation to the rest of the store as it is not directly boiler/stove heated, enabling the maximisation of solar thermal gains. An exception to this is made where the store is configured for partial or fully pumped wood /solid fuel input, and store heating is of the full volume including the coil region. This is because the store is sized to safely accommodate a full burn from the stove at maximum output, and because the stove’s operation will generally coincide with periods of minimal solar gains.

Other heat sources or input modes will generally rely on convection of heat to the top of the store:

• Gravity wood burner: The Flow connection will generally be 200 – 300mm below the top of the cylinder. This is because the flow temperature is unregulated, so when in operation, if the flow temperature is below that of the water presently sitting in the top of the store, this will convect down below it to a region that matches it. If however it matches or exceeds the upper temperature, this flow will rise to the top of this store. This process prevents the hottest water at the store top from being displaced or diluted by lower temperature water entering the store, in turn disrupting DHW delivery.

• Solar Thermal: A solar thermal coil sits at the base of the store in a region that is not influenced by other heat inputs or demands – i.e. no heat input or heat load tappings are connected in this region (excepting partial/fully pumped wood & solid fuel stoves). This permits the coil to sit in a relatively cool region of the store. Heat from the solar panel array will only be transported down & through the coil if the panel temperature exceeds that of the water immediately surrounding the coil, and a defined minimum value. In a heating phase, the water surrounding the coil starts to heat and once it exceeds the temperature of the water around it, it convects upwards, displacing cooler water downwards. The hotter the coil / array can heat the store water, the higher this heat rises/convects upwards & hotter the store ultimately gets.

• Electric immersion heater: Standard immersion bosses are located at approximately mid-way down the store. When energised, the immersion element heats the water immediately surrounding it, and store heating, by convection, is then the same as described for solar thermal.