Heatbank Xcel Standard Assemblies

CONTENTS AND HISTORY

This page is currently a Work In Progress. 20-02-17

This page is intended to form a repository of information for the various standard assemblies that constitute an Xcel thermal store in its various permutations. It is also intended to form a kernel of content that will form an up to date set of Installation and User Instructions for the Xcel.

X2009-2-22

Mains pressure domestic hot water via plate heat exchanger: This assembly generates domestic hot water (DHW) that is supplied to the taps and showers in the property. The assembly comprise a plate heat exchanger (PHE); a circulation pump; a flow switch; a blending (tempering valve).

It generates hot water only at the moment it is required when a tap is opened and its operation is similar to that of a combination (‘Combi’) when in hot water mode.

When a hot tap is opened, water starts flowing through the assembly and is sensed by the flow switch. This turns the circulation pump on which starts to draw primary hot water from the top of the cylinder and through one side of the PHE; simultaneously, cold mains water is flowing through the other side of the plate in the opposite direction. As the two channels of water pass each other, heat is transferred from the primary side to the secondary, cold mains side, and this cold water is transformed into domestic hot water. This passes out of the plate, through the blending valve to limit its temperature, then on out to the running outlet.

Under normal use patterns, there should always be sufficient energy stored in the top of the cylinder to provide small quantities of hot water at any time of day or night, however when taking showers or filling baths it is advisable to have the gas boiler available to provide a back up energy source. (See sections X2009-7; X2009-8; X2009-18A)

Installation

• Check the incoming cold mains water pressure. Although the plate heat exchanger is able to withstand static pressures of up to 10Bar, it is recommended that if the pressure is in excess of 6 Bar, that a pressure reducing valve is installed upstream of the cylinder to prevent excess pressures at the outlets in the property. Additionally, all fittings and appliances connected to the mains should be rated at 50% higher than the mains pressure.
• Although operation at lower pressure is possible, it is recommended that a minimum cold mains pressure of 1 Bar is connected to the unit to deliver satisfactory performance though its full range. Flow rate performance is relative to pressure and at lower values, poor flow rates to taps and showers may be the result.
• The characteristics of the plate will help to reduce the rate at which scaling up occurs, where the store is installed in hard water areas. However it will not ultimately prevent it; therefore it is recommended that scale inhibiting or water softening equipment is installed on the incoming supply to the property in locations where scale build up is a problem.
• A cold mains water supply pipe from the incoming supply must be installed up to the unit, such that it can be connected to the flow switch pre-plumbed to the cylinder. This pipework should be installed in 22mm copper.
• An isolating valve must be fitted to the cold mains supply upstream of the cylinder, in the vicinity of the unit (e.g. within the cupboard it is located in), and in clear sight.
• A Y-pattern strainer (supplied loose) must be fitted to the cold mains supply to the cylinder, downstream of the isolating valve and in a position to permit servicing.
• The cold mains supply pipework must be connected to the unit such that the body of the flow switch sits completely vertically, and thus permit reliable operation. If it sits out of line of the vertical, this may cause the switch to activate inconsistently and fail to run the heat exchanger pump.
• The thermostatic valve fitted to the unit is to limit the temperature of DHW that is delivered to the outlets around the property, and thus reduce the risk of scalding. Note that the design operating temperature of the unit (the temperature of primary water stored in the cylinder) is in the region of 70° – 75°C and under certain conditions, the plate can deliver DHW within a few degrees of this to the inlet of the blending valve. The valve should therefore be adjusted to deliver a maximum temperature of 55°C, or a value of the client’s preference, and can then be locked to prevent tampering.
• The plate heat exchanger pump should be set at a speed that permits adequate DHW delivery at the largest outlet in the property (or the combined outlet of the total of the largest outlets wished to be drawn simultaneously - if multiple draws are required). Note that the maximum 35 litres/min is only possible with a store held at a minimum 75°C. The faster the pump speed, the higher the potential DHW flow rate. The pump should not be set at a speed higher than is necessary, to prevent a reduction in efficiency and to permit greater draws of DHW from the store. The speed dial should be set in the right hand half of the range (constant differential pressure).

image of pump face here

Performance

Maximum DHW flow rate: 35 Litres/min
Maximum possible DHW temperature: 65°C
Maximum recommended DHW temperature: 55°C
Minimum flow rate: 3 Litres/min
Maximum heat transfer rate: 100KW (see attached data sheet)

Component List

Component	Make / Model	Part Code	Data Sheet
Plate Heat Exchanger	SWEP IC8 x 40	7066554
Pump	Wilo Yonos PARA RS 25/1-6	7070047
Flow Switch	Sika VKX15	702307
Blending Valve	Altecnic Mixcal III TMV 2	70200015