System HS
Vented Store & Primary System, Sealed Solar System
250 litre storage
500mm diameter x 1800mm high
Ref.: J782
|
|
Solar Heat Bank Thermal Store System HS |
||
|
Vented Store & Primary System, Sealed Solar System
250 litre storage |
|||
Copyright Dedicated Pressure Systems Ltd.,
1998
Patent Applied For
The System HS Solar Heat Bank Thermal Store has been designed to fully integrate a domestic solar system with a mains pressure hot water system, a typical radiator system, and a gas boiler.
To simplify the job of installing all these systems, we have taken all the required system components and fitted them to a 250 litre Heat Bank Thermal Store. These components are connected with the necessary pipework and are factory wired to a fitted wiring centre. This prevents costly, and possibly dangerous, mistakes from being made during installation.
In addition, any servicing engineers that come up against the system will benefit from the availability of full documentation on the entire system and how it works, will be able to draw on our knowledge and help should it be required, and can be assured that components have been installed with servicing in mind. - all too often servicing engineers end up having to drain down entire systems just because a pipe has been positioned in front of the component the need to get to.
List of system components:
Solar System Controls
The System HS Heat Bank Thermal Store is fitted with a solar finned-copper coil and standard solar system controls as supplied by AES. Controls can be fitted however to connect to any make of solar panels. The solar system is sealed, requiring an expansion vessel, pressure relief valve, pressure gauge and filling loop for correct operation. We have kept the solar system separate in this way because of the pressures required to force water up to panels on the roof, and also because the solar system water must be treated with anti-freeze. Combining the water in the solar system with the water stored in the Heat Bank Thermal Store would require us to treat the water in the Heat Bank Thermal Store with anti-freeze also, which would be too expensive.
To protect against over-filling, and to make servicing easy, we have fitted a pressure reducing valve onto the mains water supply to the solar filling hose. This will prevent the solar system from being filled to a higher pressure than is set on the pressure reducing valve, even if the person doing the filling forgets to watch the pressure gauge as the system fills.
The other solar system controls that are required are the circulating pump, flow control (AES), solar controller (AES), and control thermostats (AES). All these are fitted and wired, needing only connection to the actual panels. No more wiring is required.
Heat Bank Thermal Store & Primary System Feed & Expansion
The Heat Bank Thermal Store, as well as the radiator and boiler circuits, are fully vented to atmosphere, filled from a feed and expansion tank built into the Heat Bank Thermal Store. The feed and expansion tank takes up the expansion of water from the Heat Bank Thermal Store and heating and boiler circuits, and is fitted with a high quality ball valve to top up the Heat Bank Thermal Store should water be lost - such as when a radiator is bled. A sealed heating system is not used as standard because they are not topped up by a ball valve - if radiators are bled then system pressure would be lost, the boiler & radiators may stop working, and unless the householder knows how to top the system up manually they will be forced into calling a plumber.
The disadvantage to using a vented heating system is that the water level in the feed and expansion tank must be higher than all the radiators, boiler and connecting pipework. Although the standard system HS Heat Bank Thermal Store has the feed & expansion tank built in, a unit can be supplied for connection to a remote feed & expansion tank. This is for use on installations where there are radiators at a higher level that the Heat Bank Thermal Store, and where the feed & expansion tank must be higher still.
Domestic Hot Water
Hot water is provided by the use of a plate heat exchanger fitted into the base of the Heat Bank Thermal Store. The plate heat exchanger transfers heat from the stored water to mains cold water, providing over 30 litres per minute of hot water at mains pressure. A Flow Switch and Pump are required for operation, and a Thermostatic Blending Valve is fitted for convenient control of the hot water supply temperature. This way of providing hot water is far more efficient than using a coil, and removes the need for any cold water storage.
Primary System
The boiler and radiator circuits have been kept separate, using a two-pump primary layout, instead of the standard single pump & zone valve setup. The first reason for is it increases system efficiency, and allows us to use stored solar energy for heating as well as hot water. Secondly, two pumps are much easier and less costly to service than one pump and a three port (or 2 two port) zone valves. Both the boiler and radiator circuit pumps are fitted and wired.
Central Heating Controls
To make installation and system control as easy as possible, we have used a Danfoss Radio Room Thermostat. This replaces the standard programmer and room thermostat setup, combining the operation of both into a single unit, allowing one to program the desired temperature at various times. Furthermore, the radio room thermostat communicates with the Heat Bank Thermal Store using a radio signal, removing the need for any wiring. The room thermostat is battery powered, using two AA batteries to provide two years continuous operation before the batteries need changing - two weeks warning is given by the thermostat. The room thermostat can also be repositioned as required, and can even be taken to bed so that the central heating can be turned on without having to get up.
The Monitor Valve
One non-standard component that we have fitted into the boiler circuit is the Monitor Valve. This control automatically regulates the return temperature to the boiler, and also ensures that the Heat Bank Thermal Store is heated from the top downwards. This is important with a solar system because one of the greatest problems is working out the balance between how much stored water you dedicate to solar storage and how much the boiler heats. The monitor valve removes this problem.
While the boiler is turned on, the monitor valve keeps the top 100 litres or the store hot, just over enough water for a bath, allowing the remaining 150 litres of the store to be used for solar. As hot water is drawn from a tap, the top 100 litres is pumped by the plate heat exchanger pump to the plate heat exchanger in the base of the unit. The plate heat exchanger extracts the heat from the store water and uses it to heat the hot water going to the taps, and once this heat has been extracted, the store water (now cold) returns into the solar section of the store. Water from the 150 litre solar section of the store moves upwards to replace water drawn from the top 100 litre section - if it is not hot enough for immediate use for hot water then the monitor valve will redirect it to the boiler for boosting to a suitable temperature.
The Monitor valve ensures that all energy delivered by the boiler is directed into the very top of the store, where it is immediately usable. As a result, recovery rates are greatly reduced, and hot water can be obtained in a very short time from cold start.
The Monitor valve provides another important advantage. It will maintain the return to the boiler at a pre-set temperature for as long as possible, which with condensing boilers is very important to keep the boiler operating in condensing mode and efficiencies high.
Wiring to Boiler
Typically, the boiler will need wiring to the wiring centre on the Heat Bank Thermal Store. If it proves difficult to run wiring from the boiler to the wiring centre then it is possible to wire the boiler separately, using a flow switch, fitted into the boiler flow or return next to the boiler, to switch the boiler on when water is pumped through it. This setup allows the gas boiler to be electrically isolated separately from the rest of the system, and removes the need to take any wiring to the Heat Bank Thermal Store except a mains electrical supply.
Boiler Backup
The Heat Bank Thermal Store unit is fitted with a 3kW immersion heater for backup use in case the boiler fails. The immersion heater will require wiring to a suitable isolating switch.
Pipework & Insulation
All pipework is fixed firmly using support brackets onto the body of the cylinder, and any pipework that becomes hot is insulated.
The Heat Bank Thermal Store itself is insulated with 50mm CFC free foam insulation.
Additional Fittings
A Y-Pattern Strainer is supplied loose for fitting into the incoming mains water supply. A hand-operated isolating valve should also be fitted into the incoming mains water supply in a position where the householder can easily get to.
Wiring
All wiring to all fitted controls is made in the factory, using high quality heat resistant cable. The wiring is cable tied to the body of the Heat Bank Thermal Store to keep the whole installation neat and tidy.
The system will require connection to a mains 240v supply, suitable fused and fitted with isolating switch.
Connections to Heat Bank Thermal Store
The following connections need to be made to the Heat Bank Thermal Store unit during installation.
Solar Overheat Protection
With solar systems it is important to consider what happens when the system overheats on a very hot day. Unless some provision is made to cool the solar system, the water in the system will continue to rise in temperature and may reach boiling point. Often, as the water expands as its heats, the pressure in the system will increase above the setting of the pressure relief valve and water will be discharged to keep the pressure from reaching unsafe levels. This loss of water must be manually replaced, and if boiling occurs then scale deposits may build up in the system reducing efficiencies.
There are two ways to protect against this. The simplest is to fit an overheat thermostat onto the Heat Bank Thermal Store which will turn on the central heating pump when the water in the store reaches 90°C. Excess heat will simply be discharged via the radiators. This method of protection relies on the electrical supply to the system being turned on.
To protect the system against solar overheat in circumstances where there is no electrical supply, a different approach must be taken. A mechanical zone valve with temperature sensor must be fitted into the solar pipework, and connected to a radiator at a higher level. As the system overheats, the valve will open allowing gravity circulation, by convection, through the radiator. As gravity circulation is not very powerful, it is important that the radiator is large enough to remove heat at the same rate the solar panels gather heat. For best results the radiator should be external to the house, possibly on an outside wall. This is the only correct way that a solar system can be protected from overheating in all conditions, without an electrical supply present.
Additional Options
In designing the System HS Heat Bank Thermal Store we have created a single system which combines everything needed for an efficient hot water, heating and solar installation.
Furthermore, the unit can be tailored to suit each installation, with options to change the shape and size of the basic cylinder, to position bosses and pipework, or to fit any additional controls that are asked for.
If required, the unit can be supplied in a basic form, with no controls fitted or wired, or can be supplied in a kit form, with the controls supplied for installation on site.
We will be happy to look at any installation and advise on what we feel is needed. All consultancy is provided free of charge.
www.heatweb.com
Details of our solar systems, and any other information on solar systems that proves to be helpful to installers, is available from our Internet site, www.heatweb.com. This site is still in its infancy, however it is updated on a daily basis and is growing rapidly.
If you have any information that you would like to share with others through our site, please feel free to post, fax, telephone or email it to us, and it will be added to the relevant pages for anyone to benefit from.