Title : DCD Heating Controller

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Contents of Page

Balancing of Central Heating
Base Area - Location
Boiler On/Off Cycling
Boiler Energy Managers and Optimisers
Boiler Types
BRE Tests - Importance
Brochure
Combi Boilers
Controller - Gravity Fed Hot Water
Controller - Location
Differentials - Temperature Switching
Energy Savings
Factory Set Programmes
Frost Thermostat
Fuel Savings
Fully Pumped System Valves
Gravity Fed Hot Water Control Valve
Gravity Fed Hot Water Installation
Hot Water Systems
House Temperature Uneven
Legionella Sterilization
Location - Controller
Location - Outside Sensor
Location - Room Sensor
Megaflow - Sensor Location
Minimum Heat Maintenance
Optimum Start
Outside Sensor - Location
Price and Ordering of a Controller
Programming - Legionella Sterilization
Programming Temperatures
Pump Control & Overrun
Room Sensor - Location
Savings without affecting Comfort
Savings in Fuel - 25% and much more
Savings on Maintenance
Sealed Hot Water Systems - Sensor

Smoothing of Central Heating Temperatures
Temperatures - Optimum Start
Temperatures - Programming
Temperatures - Central Heating Smoothing
Temperatures - Boiler On/Off Cycling
Temperatures - Switching Differentials
Temperatures - Central Heating Settings
Temperatures - Water Heating Settings
Temperatures - Legionella Sterilization
Temperatures - Outside Display
Thermostats - Usage and Types
Towel Rails
TRVs (Thermostatic Radiator Valves)
Underfloor Heating Zones
Underfloor Heating Valves
Unvented Hot Water Systems
Valves - Gravity Hot Water
Valves - Mid Position
Valves - Two Port
Valves - Underfloor Heating
Water Cylinder - Sensor Location
Weather Compensation
Zones - Parts of a House or Building
Zones - Upstairs & Downstairs
Zones - Underfloor Heating
Zones - What about more
   
Sales and Technical Enquiries Return to Index (Home Page)


Combi Boilers

Is a DCD Heating Controller suitable for use with a Combi Boiler ?

It is sometimes thought that the benefits of a DCD Heating Controller cannot be obtained with a Combi boiler. This is not correct. A special controller mode of operation is provided and all the central heating benefits apply when combi boilers and combi condensing boilers are used. Although water temperature control is not needed when a combi boiler is installed, the added advantages to be gained by installing a DCD Controller should not be overlooked. The programmed control of central heating and tight temperature smoothing control, which is discussed below, applies equally to systems based on combi boilers as to standard central heating systems.

Combi heating systems, with their powerful boilers that quickly heat up water on demand, are normally oversized for central heating purposes; indeed, with small flats, the boiler can often be as much as three times more powerful than one that would be capable of keeping the flat adequately warm in the coldest weather.

In central heating systems where the boiler is directly controlled by a room thermostat, residual heat in the boiler, radiators and pipework, continues to be transferred into the building, long after the thermostat senses that the required temperature has been reached and the boiler has been turned off. With a combi boiler, this faster build up of heat is much greater than with a standard boiler, particularly in milder weather, and results in heating the building appreciably above the temperature required.

The degree of control offered by predicting the optimum boiler firing time ensures that the building's occupants are kept more comfortably warm and that fuel economies are made by eliminating overheating.

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Temperatures - Programming

What are the benefits of being able to programme different temperatures for different times of day ?

Central heating users want their heating at the lowest level at which they feel comfortable, but this level varies according to the time of day, and to whether they are active or relaxing.

The vast majority of control systems for central heating are not able to satisfy these needs. They do not recognise different weather conditions and are not able to start heating in order to get the house to the required temperature at the time that it is needed. Few systems can vary temperatures according to time of day for both central heating and water heating under programmed control. Many allow central heating thermostats to be changed manually on an ad hoc basis, but do not return to a preset level automatically, and very few allow adjustment of water heating temperatures on an ad hoc basis.

For water heating in a family environment, a relatively high temperature may be needed at a time when more than one bath might be required. A lower temperature is normally desirable when showers are taken, in order to avoid the build up of limescale in the shower. Even lower temperatures may be required at other times in the day for hand washing, etc.

By comparison, the DCD Heating Controller provides variable temperature programming, and anticipates or optimises the start time for each programmed temperature setting according to the weather, in order to get to the required programmed temperature at the right time. Different temperatures can be programmed for different times of day and for different days of the week, for both heating and hot water. Ad hoc changes to cater for entertaining and occasional needs may be made quickly and easily, with simple plus and minus buttons that amend the temperature settings and the time that the current programmes start and finish. Also, unless otherwise set, operation of the system returns to automatic programmed control when the current programme ends. This makes it unnecessary to restore an original setting when a temporary requirement finishes. Factory Set Programmes are provided for initial operation - see below.

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Temperatures - Switching Differentials

What is a Thermostat's Switching Differential, and what is its relationship to the overall heating differential quoted for the DCD Heating Controller ?

Thermostats for the control of central heating are designed to switch On at one point and to switch Off at a higher point, thus bringing heating into action at the lower point and stopping it when the higher point is reached. The temperature difference between the switching On and switching Off points is referred to as the Thermostat Switching Differential.

Operation of a thermostat is based on metal that expands or bends, according to temperature, and which closes/opens contacts to operate the On/Off switching of boilers in central heating systems. The time to warm up or to cool down the thermostat, in varying conditions, affects its accuracy, but sensitivity performance can be improved by use of a built-in accelerator heater. However, the availability of electronic sensors now makes it possible to design a fast acting electronic thermostat that will, in theory, quickly and accurately detect very small temperature changes.

A fast acting electronic sensor (electronic thermostat) may be used in a central heating system to keep the temperature more accurately than a conventional metallic thermostat. However, in practice, a reasonable switching differential is needed to moderate sensitivity so that the boiler or heater is not rapidly switched On and Off (cycling), due to draughts and air currents. A switching differential of 0.6C degrees is commonly regarded as necessary, but 0.3C degrees may be used in specialist devices.

Unfortunately, instantaneous control of temperature with an electronic thermostat is not possible. Heat cannot be delivered immediately when On is set, and delivery cannot be stopped when Off is set. At the start of a heating cycle, a delay arises because it takes time to fire and raise the boiler temperature, to transfer and circulate heat around the heating system, and more time to radiate or transfer it to the space to be heated; during this time, in cold weather, the temperature will fall further with the result that temperature undershoot will occur before the heat that has been called for can be delivered. At the end of a heating cycle, heat built up in the system will be dissipated or radiated after the required temperature is reached and Off is set, and this will result in temperature overshoot - this is usually greater in systems with combi boilers or high powered boilers, than those with low powered boilers or older houses. The situation is even further complicated because heat transfer delays vary according to the weather, the characteristics of the building being heated and a variety of other factors.

Briefly, by way of example to illustrate the point, consider a house with an electronic thermostat that can keep the temperature to 0.3C degree, with a switching differential of 0.6C degree, an undershoot of 0.2C degree and an overshoot of 0.3C degree. When heat transfer delays are taken into account, the system will have an overall heating differential of rather more than 1.1C degrees, and very considerably more in many houses. This is not satisfactory as few people can remain comfortable if the temperature fluctuates by more than a degree.

By contrast, the DCD Intelligent Heating Controller, with its sophisticated temperature smoothing system, that regulates boiler firing and takes account of the factors discussed above, has been demonstrated by BRE as being capable of maintaining the temperature to within an overall heating differential of 0.1C degree in a well insulated house. This is a very small variation that nobody notices and which contributes to the outstanding comfort and economy provided by the DCD Heating Controller.

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Minimum Heat Maintenance

What is Minimum Heat Maintenance ?

In addition to monitoring the room temperature, the Room Sensor can detect whether the surrounding temperature drops below a preset level - this is factory set at 12C degrees. If this happens, the boiler and pump runs for five minute periods, at intervals of twenty minutes, to maintain a minimum level of heating for the protection of pipework and to safeguard sensitive equipment, furniture and health. This is done even if central heating is not programmed to run when the temperature drops to this level, or it is set to Off. Please note that this is not the same as frost protection for the boiler and pipework, which is operated by an optional Frost Thermostat that may be set to any desired temperature.

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Boiler On/Off Cycling

What is Boiler Cycling and why is it necessary for it to be controlled ?

An unnecessary series of boiler firing bursts to maintain the temperature of boiler and connecting pipework, under control of the boiler thermostat, is termed boiler cycling. This can happen when heating controls are not fitted or when the available controls are inadequate.

Firing up a boiler requires a given amount of fuel, so a heating system will operate more economically if the number of cycles is reduced. Furthermore, since the life of boilers and pumps is related to the number of times that they are started up, and not to the total operating or heating time; they will last longer and maintenance will be reduced if the number of On/Off cycles is minimised.

What causes Boiler Cycling and what can be done about it ?

In the case of Water Heating with a gravity fed system without a thermostat and control valve, boiler cycling regularly occurs because the boiler continually tops up the heat of the water in the boiler jacket and pipework in order to maintain the temperature. With a thermostatically controlled system, with a fixed thermostat setting, cycling can still occur as the rate of water temperature increase slows down while achieving a high water temperature. When this happens, the boiler thermostat will frequently cut out to prevent the boiler from overheating.

With Central Heating, if a room thermostat is not fitted and temperature control is entirely with thermostatic radiator valves, regular boiler heating cycles are called in order to maintain the temperature of the water in the pipework. Where an electronic thermostat is installed to maintain temperature control within fine limits, cycling will happen if there is an insufficient On/Off differential to provide reasonable stability and avoid interference from draughts and air currents - see Switching Differentials. Ideally, electronic thermostats require built-in intelligence to control the number of boiler cycles per hour but, the difficulty then is to maintain the room temperature required by using the full power of the boiler when it is needed.

The DCD Heating Controller overcomes these difficulties by providing variable temperature facilities and incorporating the necessary intelligence to control boiler cycling for optimum fuel utilisation with extended boiler and pump life, while still keeping the room temperature to within 0.1C degree. Its unique Temperature Smoothing feature provides comfort with economy - see below.

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Boiler Energy Managers and Optimisers

Does the DCD Heating Controller optimise boiler firing ?

Yes. The DCD Heating Controller smoothes out heating to avoid temperature fluctuations and optimises boiler firing as part of its temperature smoothing feature - see below. However, a sophisticated fast response mechanism quickly deals with changes in temperature requirements and temperature drops, in order to provide maximum comfort at all times, yet the boiler is never cycled or fired to sustain the temperature of heating water in the pipes and radiators when there is no real demand for heating.

Is a Boiler Energy Manager or Optimiser the same as a DCD Heating Controller ?

No. Generally, a Boiler Energy Manager will adjust the temperature of the water heated by the boiler, in relation to the outside temperature by reference to sensors that provide information on boiler return flow water and outside temperatures. To some extent, automatic overrides may also take care of demands for domestic water heating, and boiler interlocks may stop boiler firing that is not needed in some situations. In terms of basic functions, they do not usually provide programmed water temperature control or variable room temperature control, so water thermostats, room thermostats or programmable thermostats and time clocks are generally required in addition. Operation of these items are not integrated into the system.

On the other hand, the DCD Controller effectively integrates all the facilities normally covered by a boiler energy manager, together with the temperature measuring and clock facilities mentioned above. In addition, it provides optimum start for each programmed temperature setting for both domestic hot water and for central heating, together with temperature smoothing and other facilities. It builds up and maintains a history of heating performance in your house for different times of day under varying temperature conditions, and it uses this history to calculate the automatic start adjustment for weather in order to get to the temperature required for each programmed temperature setting, for the time that you set for both central heating and domestic water heating. It is important to remember that it may take your boiler a few minutes to raise the house temperature by a single degree in mild weather, or as much as an hour and a half in very cold weather;  this is all taken into account automatically by the DCD Controller. Once the required house temperature is achieved, it then optimises boiler firing to keep the temperature there, extremely accurately. Your radiators are kept warmer when the weather gets colder; indeed, especially in variable Spring and Autumn weather, most users feel their radiators to get a quick indication of how cold it might be outside - the warmer the radiators the colder it will be. Overheating by even a fraction of a degree, or heating when heat is not required, is expensive waste.

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Temperatures - Central Heating Smoothing

What advantage is there in being able to maintain central heating temperatures within very tight limits ?

Many thermostats are not able to maintain room temperature to within less than two or three degrees; a good one will keep it within a degree and an electronic thermostat can be expected to keep the temperature within around half a degree of the temperature at which it is set. This is not good enough.

A person who sets a thermostat to bring on the heating at the point where he or she feels uncomfortable will feel too warm when the temperature rises a degree above the level that has been set. Overheating in this way results in waste of fuel, but it also gives rise to frustration when it becomes necessary to vary temperature settings during a day, or during an evening, because one is not comfortable.

The DCD Heating Controller optimises boiler firing and smooths out heating fluctuations, so that the temperature is kept to within a tenth of a degree of that set. When heating is required, radiators are warmed to give out the heat that is needed, the colder the weather the warmer the radiators become and hot/cold radiator heating is avoided. Heating beyond the temperature set by the user does not happen. This feature provides maximum comfort under all weather conditions, and it also eliminates wasteful overheating.

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Temperatures - Central Heating Settings

What central heating temperatures are normally needed ?

In order to feel comfortable at all times, it is necessary to provide different temperature settings for different times of the day. For example, one temperature may be needed for getting up in the morning, no heating may be wanted when people are not at home, while a lower temperature will be wanted when people are active around the home, a temperature that is a bit higher will be needed in the evening and perhaps a degree higher when they settle down to watch television.

Comfort should always be given the highest priority. The greatest fuel savings on central heating are made automatically when people are made comfortable and not overheated.

With the DCD Heating Controller, heating is only run when it is required. It is not started earlier than is necessary to reach the right temperature at the right time. The temperature can be set lower for when people are active and raised when they are sitting down and relaxing. Furthermore, accurate temperature maintenance gives maximum comfort at all times.

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Temperatures - Water Heating Settings

What water heating temperatures are normally needed ?

A typical hot water cylinder thermostat is set by the installer and, due to its location, it is normally impractical for a user to vary it according to changing needs on a day to day basis. Furthermore, most electromechanical thermostats for hot water cylinders have a switching differential of 8C degrees.

For most purposes, it is unnecessary and often unsafe, especially when children or elderly people are around, to raise the hot water temperature above 45C degrees.

So, while a temperature of 45C degrees is satisfactory for most water heating purposes, and a temperature of 52C degrees may be satisfactory for periods when more than one bath is to be drawn off in quick succession, it is commonly regarded as necessary by installers to set the thermostat temperature to 60C degrees in order maintain availability of hot water for all conditions.

It is wasteful for the temperature to be constantly raised by 15C degrees above the level that is needed. Most hot water systems will take at least twice as long to raise the temperature from 45C degrees to 60C degrees as they take from 30C degrees to 45C .

The DCD Controller maintains water temperature to within a degree of the set level and allows different temperatures to be programmed for different times of the day. It also makes it easy to raise the temperature whenever it is necessary to heat up water to a higher level than usual in order to meet exceptional demands. It is wasteful to heat up and maintain stored water at a hotter temperature than needed.

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Legionnaires' disease

How does the DCD Controller handle the health risks attributable to Legionellosis ?

The Health & Safety Executive (HSE) states that Legionella are killed at temperatures of 60C degrees and above. Since the DCD Controller has the flexibility to run domestic hot water programmes at varying temperatures, a programme for Legionella Sterilization can be set to run at the critical temperature for a period of, say, five minutes weekly or, whatever frequency is thought to be desirable.

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Temperatures - Outside Display

Why might I want to know the Outside Temperature and how is it shown ?

The Outside Temperature is displayed when the appropriate button on the front panel is pressed.

The controller always gets your home to the same inside temperature, regardles of weather conditions, at the same time each day. It can therefore be important, before going out of the house on a dark morning, to know, for example, whether the outside temperature is +4C degrees or -4C degrees.

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House Temperature Uneven

Why are some rooms in my house too warm while others are not warm enough ?

If you are not restricting the heat in your cooler rooms with the radiator control valve or a thermostatic radiator valve, then the most likely cause is that your central heating is not properly balanced - see below.

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Balancing of Central Heating

Why does my central heating system need to be balanced ?

The important thing about central heating is that it aims to heat the whole house from a single source but not, normally, to heat the whole house to the same temperature. This is done by heating and controlling the temperature in a base area that is always in use (perhaps your hall) and by balancing all other areas to this area.

So, for example, you may arrange to have a room temperature in your living room that is a degree higher than in the base area, and for the temperature in your bedrooms to be a degree lower. Balancing is done, hopefully, at the design and installation stage when the appropriate sizes of radiators are selected to achieve the desired result. However, small adjustments can be made by adjusting individual radiator shut-off valves to restrict the flow of heating water in order to get a satisfactory balance.

In extreme cases, such as may be encountered in older heating systems, it may become necessary to change one or more radiators for modern high output radiators in order to put things right. If you are putting in a DCD Controller and are not happy that you have been able to get the balancing right, it may be best to install the controller and to run the system for a bit and to then check again to make sure that you do in fact need to make radiator changes

So you get to a situation where a change to the temperature setting for the base area, will cause the temperatures for all rooms in the house to be raised or lowered automatically, in sympathy.

In normal operation, temporary adjustments may be made from time to time. For example, the radiators in an unused room may be turned off or turned down by using the radiator control valve or Thermostatic Radiator Valve (TRV), if fitted.

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Zones - Upstairs and Downstairs

Is it an advantage to have separate zones for upstairs and downstairs ?

It is sometimes thought that there may be advantages to be gained by operating separate zones for upstairs and downstairs. The idea being that savings may be obtained by heating the upstairs zone only first thing in the morning and in the evening, and not during the main part of the day when bedrooms are not being used.

Our experience has been that, in most houses, operation of zones is not generally a good idea and the fuel saving is marginal. Cold air may flow from unheated areas to heated areas, such as from upstairs to downstairs, thus causing convected draughts which affect overall comfort. When rooms are not heated, doors need to be kept shut to minimise the effect of convected draughts. This discipline is virtually impossible to maintain in a family environment.

Experience has been that people who have previously operated separate upstairs and downstairs zones and who have put in a single DCD Controller with the intention of re-instating their separate zones as a second stage, have never done so. They have all been pleased with the results that they have obtained and say that they do not see the point in having separate zones, when a single DCD Controller is so efficient in providing whole house comfort and saving energy.

It must be remembered that the DCD Controller offers variable temperature settings throughout the day to meet the changing needs in a home for variations in occupancy and activity. This has a whole house impact.

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Zones - Parts of a House or Building

Will a DCD Controller handle zones ?

Technically, a DCD Controller will control two zones - one for central heating and one for hot water. If you need to operate a further zone, DCD Controllers can be run in parallel or linked to provide full optimising and temperature maintenance features. Where more than one controller is installed for central heating, each controller will optimise its own zone independently.

Separate zones should normally be operated for swimming pools and conservatories, and may be an advantage if part of a house is operated as an office or as a flat when the occupants have different requirements to the rest of the building. Other separate zone applications include multi-occupancy buildings, and buildings where parts have different characteristics, such as a new extension built onto an old house, when it may be advantageous to optimise and control the old and new parts separately, to take account of differences in construction materials and insulation.

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Zones - Underfloor Heating

Underfloor heating manufacturers recommend the use of zones. Are these necessary ?

Generally, zones in a house or building, as discussed above, cover parts or sections of a building. They are quite different from floor heating zones for underfloor heating.

Underfloor heating zones relate to floor areas in which heating pipes are laid to distribute heat and, as such, may be compared with radiators in a conventional central heating system. A valve may be used in conjunction with a thermostat in such systems to control an underfloor heating zone and to perform a similar task to that of a Thermostatic Radiator Valve - see TRVs below.

However, several underfloor heating zones, normally grouped and controlled by a manifold, may be treated as a single zone and controlled by a DCD Controller in the way that is described above.

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Zones - What about more

Can you control more than one heating zone or channel with a controller ?

As already described above, technically, a DCD Controller will control two zones - one for central heating and one for hot water. If you need to operate a further heating zone(s), DCD Controllers can be run in parallel to provide full optimising and temperature maintenance features. Where more than one controller is installed for central heating, each controller will then optimise its own zone independently.

At the planning stage, we looked at the possible advantages to be gained by operating separate zones for upstairs and downstairs. The idea being that savings might be obtained by heating the upstairs zone only first thing in the morning and in the evening, and not during the main part of the day when bedrooms are not being used. We found that, in most houses, operation of zones was not generally a good idea and the fuel saving is marginal. Cold air may flow from unheated areas to heated areas, such as from upstairs to downstairs, thus causing convected draughts which affect overall comfort. When rooms are not heated, doors need to be kept shut to minimise the effect of convected draughts. This discipline is virtually impossible to maintain in a family environment.

In practice, our experience has been that people who have previously operated separate upstairs and downstairs zones and who have put in a single DCD Controller, together with TRVs (see below), with the intention of re-instating their separate zones as a second stage, have never done so. They have all been pleased with the results that they have obtained and say that they do not see the point in having separate zones, when a single DCD Controller is so efficient in providing whole house comfort and saving energy.

It must be remembered that the DCD Controller offers variable temperature settings throughout the day to meet the changing needs in a home for variations in occupancy and activity. This has a whole house impact.

However, in some circumstances, it may be advantageous to control separate zones with separate controllers. See above.

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Gravity Fed Hot Water - Motorised Hot Water Control Valve

Do I need a motorised water valve in a system with gravity fed hot water and pumped central heating ?

Although a DCD Controller may be installed without a control valve for hot water, this is in fact an essential later enhancement if maximum benefits are to be obtained, and should be introduced at the first opportunity.

A hot water control valve will enable the boiler to be run at its maximum, when it will operate most efficiently and heat your home and hot water in the shortest time. The temperature of your water at the taps can then be programmed to whatever you choose for different times of day.

The DCD Installation Instructions describe how you connect valves in a system with pumped central heating and gravity fed hot water. One valve is needed in the water circuit with a gravity hot water system for temperature control, but one may also be put in the heating circuit to stop ‘creep' in the summer months. It is in fact vary rare for a valve in the heating circuit to be needed.

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Fully Pumped System - Valves

What Control Valves might be used ?

The Controller will directly handle Honeywell V4073 Mid Position Valves (commonly and wrongly referred to as diverter valves, and sometimes described as three port valves) and equivalents - see diagram in Technical Information Section. These enable the water heated by the boiler to be directed either to hot water heating or to central heating, or to both together.

Alternatively, separate 'Two Port' Valves (sometimes described as in-line valves) may be handled directly - such as the Honeywell V4043 and equivalents. Typically, one valve is then used to control hot water heating and another for central heating, but other arrangements may be configured for various purposes. Two-Port Valves are mandatory for most types of pressurised hot water systems and are normally best used when separately controlled zones are featured, when controlled towel rail heating is provided, and when underfloor heating is involved.

In a typical arrangement, with one two-port valve controlling central heating and another the water heating, the boiler water pump should be wired through the valve contacts - in parallel. This ensures that the pump cannot be run in the event of one or both valves not being open as the result of a fault - something that is more than likely to happen sometime in the life of the system.

Where a separate pump is provided for water circulation in an underfloor system, power for this is normally provided from the ‘Heat' & ‘Neut' terminals (to which the heating control valve is also wired) on the DCD Controller. The DCD Controller provides a minimum of a minute's overrun after each boiler firing cycle but, in some cases, additional overrun may be required for the underfloor heating pump to ensure thorough circulation of heated water; where required, this can be provided by incorporating a delay module (of the type used for bathroom fans to enable them to be run on after a light or shower is switched off).

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Pump Control & Overrun

What is Pump Overrun ?

Pump Overrun is the term used for when the pump is run for a period after the boiler is switched off at the end of a period of heat demand.  See Technical Information for further information about how this is handled by the DCD Controller.

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TRVs (Thermostatic Radiator Valves)

Do I need TRVs ?

Except in the base area, it is normally advantageous to use TRVs as a temperature limiting device to handle rooms that may become overheated occasionally by solar gain, typically on one side of the house on days that the sun is exceptionally strong, or when a room can be overheated by supplementary heating, such as from an open fire in a living room, or from cooking in the kitchen. An individual bedroom occupant may prefer to limit the bedroom temperature, etc.

A TRV should not be used in the area in which the Room Sensor is installed (base area), where the temperature is directly regulated by the Controller, or in open plan living areas which effectively form part of the base area. Because it is essential that the controller should be in full command of the heating in the area in which the room sensor is located, any TRV fitted to a radiator in the base area prior to installation of the controller should be kept permanently set to its maximum setting.

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Controller with Gravity Fed Hot Water - Installation

Can I install a DCD Controller with an existing gravity hot water and pumped central heating system ?

Yes. You can install in two easy stages if you wish.

The first stage can be to wire up the controller without any plumbing changes - many people do just this for a start. You will need to drill a hole in an outside wall to take the DCD outside sensor, and to fit the DCD room sensor - this can replace your room thermostat, if you have one, using the existing wiring. The supplied sensors use 5 volts, so bell wire or telephone cable can be used for them if you do not already have existing wiring that is suitable.

The second stage would then be to put in a water control valve in your gravity hot water feed and, at the same time, mount the DCD water temperature sensor on your hot water cylinder. This will enable the controller to control the water temperature, so that water is not heated unnecessarily and, at the same time, enable you to run the boiler more efficiently at its maximum temperature (for less time) for heating your house more quickly. Wiring diagrams are included in the installation instructions - all wiring to the controller is on a point to point basis - there is no crossover wiring and no need for a wiring crowsnest in a junction box or wiring centre.

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Controller - Location

Where should the Controller be located ?

Typically, if the boiler for a central heating system with radiators is installed in the kitchen on an outside wall, it will normally be convenient to locate the controller adjacent to the boiler, or outside the boiler cupboard if the boiler is fitted in a cupboard. It should be at eye level and in a lighted position where the display can be easily read by the user.

The most important factor to be considered when deciding where the controller should be placed is that there will probably be at least one person in the house who will wish to regularly read the outside temperature from the controller display. Bear in mind that the controller will bring the inside of the house to the same temperature at the same time every day, and that many people need to have some idea of the outside temperature before they go out of the house. Particularly on dark mornings, when outside temperatures may vary considerably from one day to the next, and when information may be wanted for a variety of reasons; perhaps to know how warm or cold it is in order to decide what clothes to wear; perhaps to decide whether there is likely to be ice outside and so have to allow extra time for traffic delays or to de-ice the car windscreen, etc.

Some installers may consider it desirable to place the controller near the boiler, to simplify installation and boiler maintenance, but this is not essential and the needs of the user should be put first. It is clearly not satisfactory from the point of view of users, who need to get to the controller frequently, for it to be located in a garage, cellar or outhouse, or for it to be placed just above the working surface in a kitchen or in an airing cupboard. The controller itself does not contain any sensors and so its operational efficiency is not affected by its location.

In short, the ideal location for the controller is where it is best placed for ease of use. Secondary considerations are ease of installation and convenience of access during boiler and central heating system maintenance checks, etc.

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Room Sensor - Location in Base Area

Where should the Room Sensor be located ?

The Controller operates by reading the temperature at the Room Sensor and controls the temperature for the whole house or flat by reference to the area where it is chosen to locate the sensor. This area is referred to as the base area.

As with a thermostatically controlled central heating system, the Room Sensor should normally be located at about shoulder height, be clear of obstructions from furniture and curtains, be in an area that is always in use and where the air can circulate freely, such as a hall or living area and where the temperature normally varies in line with the temperature of the house or flat as a whole. It should never, for example, be placed in a kitchen where it can be affected by heat from cooking, or in a little used dining room or store room. As far as possible, it should be clear of radiators and be out of the way of draughts and local temperature fluctuations, such as may arise near to stairways, windows or doors, or which may be caused by the opening and shutting of windows or external doors. It should not be put in a position where the temperature may be affected by direct sunlight, or by the use of occasional heat from supplementary gas or electric heating, or by other appliances, such as a clothes washer or drier, that may be used from time to time. Nevertheless, a main living room may be appropriate in some cases, especially in an open plan house layout. In practice, compromises have to be made and the perfect location is seldom available.

Main living and other areas are centrally heated in relation to that area. It is important, therefore, that the radiator settings in the base area should not be restricted either manually or automatically, such as by the use of Thermostatic Radiator Valves (TRVs) or underfloor heating thermostats.

However, if the some areas are underheated by comparison with the base area, perhaps because larger base area radiator(s) than needed are installed, it may be necessary to reduce the heating rate in the base area by slightly closing the radiator shut-off valve(s) in order to improve the balance of the heating system and to distribute proportionately more heat into these cooler areas.

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Hot Water Cylinder Sensor - Location

Where should the Hot Water Cylinder Sensor be located ?

Standard practice is to mount the sensor on the side of the cylinder and about eighteen inches above its base, but this does not of course measure the temperature of the water that may be drawn off by a tap at any particular time. The relationship of the tap water temperature to the sensor reading will be affected by the size and type of cylinder used, and to a lesser extent by the fixing method chosen for attaching the sensor to the cylinder. In most cases, the sensor will never be secured to the bare metal of the cylinder, but simply secured in a hole cut in the insulation material and held in place with the strap that is provided with the sensor.

With Megaflow systems, sealed or unvented hot water cylinders and thermal storage systems, the sensor is normally fitted within the covered space provided for a thermostat on the side of the unit. Where a thermostat is already installed, this should be left in place and, wherever possible, wired in series with the DCD provided sensor. Further information available by email.

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Outside Sensor - Location

Where should the Outside Sensor be located ?

In practice, due to the operation of its sophisticated software, it has been found that the location of the outside sensor has only a marginal effect on the efficient working of the DCD Controller's Optimum Start features. Typically, a controller is most often fitted by the side of the boiler, but clear of the boiler flue, on an outside wall; the outside sensor, for ease of installation, is then fitted on the same wall by drilling a hole straight through from behind the controller.

However, in order to display a fairly accurate outside temperature reading (see Temperatures - Outside Display), the Outside Sensor is best located on an external wall in a place where it is protected from wind, sunlight and conditions that can give rise to false temperature readings.

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Fuel Savings without affecting Comfort

How does the controller manage to save fuel without making economies that affect comfort ?

There are three main ways in which the controller saves fuel.

Firstly, Optimum Start on every programme, for both heating and hot water heating, ensures that heating is never started earlier than is necessary to provide the selected temperature at the right time, whatever the weather or hot water requirements may be. This enables significant savings to be made with heating in Spring and Autumn, and with hot water in the Summer.

Secondly, maintaining tight temperature control to within 0.1C degrees prevents fuel waste caused by the overheating which occurs in systems with a conventional thermostat, or with a sensor that is not operated with temperature smoothing optimisation facilities. These systems will allow temperature fluctuations by a degree above the set level, or even more in many cases.  Since people endeavour to set a heating temperature at which they will feel comfortable, all heating above the level set is waste.

Thirdly, programmed control enables temperatures to be maintained at varying levels throughout the day, according to needs. By comparison, a thermostat will be set at a constant level and the house heated to this temperature whenever heat is required. This level would normally be set relatively high, at the comfort level needed for sitting and relaxing in the evening. Similarly, there is no need to heat hot water throughout the day to a level that may be required only for a short period, to provide enough hot water to be drawn off for baths.

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Savings on Maintenance

What is the impact of the controller on maintenance costs ?

The controller always maintains a minimum temperature of 12C degrees, even when heating is turned off. This ensures that the fabric of the building and its contents do not deteriorate as a result of condensation or dampness, which can occur when a property is left unoccupied or when adequate heating is not maintained.

The ability to lower the temperature of hot water to the level that is required at the taps, reduces the build up of limescale. This occurs when water is continually heated to an unnecessarily high level and affects hot water cylinders, pipes, taps, thermostatic mixer valves, showers, etc.

The controller regulates boiler cycling to reduce maintenance costs and extend boiler life. The pump and valve exercise features are designed to avoid build-up of sediment, which can overload the starting torque of the pump, causing damage to it.

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Optimum Start and Weather Compensation

Does the DCD Controller provide Optimum Start and Weather Compensation ?

The DCD Intelligent Heating Controller is an Optimising Controller with full Weather Compensation. It optimises on every programme in the day, not just the first one, and it optimises central heating programmes and hot water heating programmes separately. You always get the temperature you ask for at the right time, whatever the weather.

Typically, in domestic housing, a time clock may be set an hour early to get the house to temperature by the time that the occupants rise in the morning and, similarly, later in the day, for an hour before they return from work, etc. This arbitrary hour to warm-up is inefficient and wasteful. It is not sufficient on very cold days, while it is often far too long for Spring and Autumn days, and milder Winter days, which represent the majority of the days in the year when heating is required

It is sometimes argued that temperature trends within a building are relative to those outside, and that it is thus sufficient for an Optimum Start system to be based on an inside or room sensor, only. This is not true.

DCD originally developed an Optimum Start system that would operate from an inside sensor and, because the level of accuracy was not as good as expected, then produced a more advanced system that would operate with an outside sensor. In trials through two Winters, it was clearly demonstrated that the system with an inside sensor was considerably less efficient than the one with an outside sensor. The basic problem was that temperature trends in the United Kingdom can change suddenly and unexpectedly, a falling temperature may change to a rising temperature, and vice versa, and such changes cannot be recognised quickly enough by an inside sensor in a modern well insulated building.

Plans to market the inside sensor system were dropped as it became evident that it was far less efficient than the outside sensor system. DCD's systems calculate optimum start for each programme in the day and allow optimum start to supersede previous lower temperature programmes as required. See also Temperatures - Programming.

It is not appropriate to regard optimum start and setback systems, relying solely on inside temperatures, as being capable of providing comparable performance to optimum start systems based on an outside sensor with true weather compensation

Further information is available in 'The Facts' , accessed from the Index Page. The following graph illustrates the Optimum Start feature over three consecutive days in February.

Optimum Start Chart

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Thermostats - Usage and Types

How do Thermostats work in a heating system ?

Operation of a thermostat is based on metal that expands or bends, according to temperature, and which closes/opens contacts to operate the On/Off switching to directly or indirectly operate boilers in central heating systems. However, the availability of electronic sensors now makes it possible to design a fast acting electronic 'thermostat' that will, in theory, quickly and accurately detect very small temperature changes.

Room Thermostats

While a fast acting electronic sensor may be used in an electronic thermostat for a central heating system, where it can react very quickly to keep the temperature accurately, this is not quite straightforward. In practice, a reasonable switching differential is needed to moderate sensitivity so that heating is not rapidly switched On and Off (cycling), due to draughts and air currents. In other words, it switches On at one temperature point and Off at a slightly higher point.

Apart from the need to have a switching differential, instantaneous control of temperature with an electronic room thermostat cannot happen. Heat cannot be delivered immediately the temperature drops when On is set, and it cannot be stopped when Off is set. This is because, at the start of a heating cycle, when a thermostat switches to On, it takes time to fire and raise the boiler temperature, to transfer and circulate heat around the heating system, and more time to radiate or deliver heat to where it is required; during this time the temperature may fall further with the result that room temperature undershoot will occur. Vice versa, at the end of a heating cycle, when Off has been set and the heating has been turned Off, heat that has been built up in the system is radiated and delivered after the required temperature has been reached, thus resulting in temperature overshoot.

To illustrate these points, for example, consider a house with an electronic thermostat that can keep the temperature to plus/minus 0.3C degree of that set. This will have a switching differential of 0.6C degree, with an undershoot of 0.2C degree and an overshoot of 0.3C degree. When heat transfer delays are taken into account, the system will have an overall heating differential of rather more than 1.1C degrees, and very considerably more in many houses. In practice, the amount of overshoot and undershoot will be much greater in cold weather than suggested in this example.This is not satisfactory as few people can remain comfortable if the temperature fluctuates by more than a degree.

These shortcomings are overcome by the DCD Heating Controller, which optimises boiler firing and smooths out heating fluctuations, so that the temperature is kept to within a tenth of a degree of that set. For example, in a radiator system, when heating is required, radiators are warmed to give out the heat that is needed, the colder the weather the warmer the radiators become and hot/cold radiator heating is avoided. Waste by heating beyond the temperature set by the user does not arise.

Underfloor Heating Thermostats and Thermostatic Radiator Valves (TRVs)

Underfloor heating zones relate to floor areas in which heating pipes are laid to distribute heat and, as such, may be compared with radiators in a conventional central heating system. A zone valve that is installed in conjunction with a thermostat, will control an underfloor heating zone and perform a similar task to that of a TRV with a radiator. This local control is necessary, except in the base area (see above), in order to provide a temperature limiting device to handle rooms that may become overheated by solar gain. It also prevents a room from being overheated by supplementary heating, such as from an open fire in a living room, or from cooking in the kitchen. An individual bedroom occupant may prefer to limit the bedroom temperature, etc.

Water Cylinder Thermostats

Most electromechanical thermostats for hot water cylinders have a switching differential of 8C degrees. So most installers set a temperature of 60C degrees in order to obtain a minimum of 52C degrees to ensure that a satisfactory amount of water is available to meet periods of high demand in a household.

It is unnecessary and often unsafe, especially where children or elderly people are involved, to raise the hot water temperature above 45C degrees. Most hot water systems will take at least twice as long to raise the temperature from 45C degrees to 60C degrees as they take from 30C degrees to 45C, so it is also wasteful for the temperature to be constantly raised by 15C degrees above the level that is normally needed.

By contrast, the DCD Controller allows different temperatures to be programmed to meet regular demands at different times of the day, and it maintains water temperature to within a degree of the set level. It also makes it easy to raise the temperature whenever it is necessary to heat up water to a higher level than usual in order to meet exceptional demands.

Frost Thermostats

The DCD Controller can operate frost protection heating in conjunction with a standard thermostat (without an accelerator) which, typically, may be located near to a boiler sited in an exposed position (e.g. a garage).

If the thermostat detects frost conditions, the heating system is run for five minute periods, at intervals of twenty minutes, to maintain the temperature in the boiler and exposed pipes at a safe level above freezing. This is done automatically, regardless of any programme or manually entered settings, whenever the temperature drops to the danger level set on the thermostat and the boiler has not been operated for twenty minutes. Please note that this is not the same as Minimum Heat Maintenance.

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Boiler Types

What types of boilers will the controller work with ?

The controller operates with boilers for all fuel types, including combination boilers (special mode of operation available) and condensing boilers. Installations include:

Natural Gas Boilers
LPG Boilers
Oil Fired Boilers
Underfloor Heating (including electric)
Condensing Boilers See Feature
Combi Boilers See Note above
Fully Pumped Systems

Systems with Gravity Fed Hot Water

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The Importance of the BRE Tests - 25% Fuel Savings, and much more

What did the BRE Tests do, and what Fuel Savings were demonstrated ?

The Building Research Establishment (BRE) has pairs of identical test houses which are insulated to a standard just beyond that required by the building regulations. Nobody lives in them and everything is run under computer control to simulate identical occupancy in each house. Mythical people in the two houses, run their cookers, their baths, wash their hands regularly, run their washing machines, draw their curtains, go out, go to bed at night, etc. It is no use testing in houses with real people as they would have different living patterns which would invalidate comparisons made during testing.

BRE ran trials with the DCD Heating Controller in their test houses; a standard central heating system of the type being used in new housing was installed in one house, and the DCD system to be tested was installed in the other house of the pair. The performance of both systems was then studied under the same conditions. It is on the basis of these tests that the 25% saving, mentioned in DCDs literature, was obtained. (The Summary of the BRE investigation is reproduced in the section on Technical Information).

Since the BRE tests were arranged to compare the DCD Controller with a standard control system, it was necessary to run both systems with similar heating programmes. The standard control system that was used for comparison had limitations that the DCD Controller did not have; for instance, in the standard system, temperatures for both central heating and hot water could not be varied for different times of the day. Therefore, the DCD Controller had to be run in a way that would produce similar levels of heating to that in the house with the standard system. Thus, the saving of 25% was demonstrated without the full capability and flexibility of the DCD Controller being utilized.

However, in user trials carried out as part of the European Commission's THERMIE Programme, which were run over a period of two years in various types of houses and with different types of occupancy (single occupants, married couples, retired couples, families with various numbers of children, etc), people said that they saved much more than 25%. This was easily established by people with prepayment gas meters, who soon appreciated their savings, as they very quickly found that they were not spending as much on heating as they had been accustomed to spend each week. It was not possible to draw conclusions from fuel consumption figures in order to compare heating costs before and after the introduction of DCD Controllers, as people's habits change and local weather conditions vary; nor was it possible to make meaningful comparisons between families living in identical houses on the same estate, since the house occupants had different living patterns.

Nevertheless, it has been shown that the DCD Controller is capable of a much greater fuel saving than 25%, when it is used to provide varying temperatures to match family needs and to avoid running heating when it is not needed. One customer, who monitored his fuel consumption for an extended period, covering both pre and post DCD Controller installation, has demonstrated a fuel saving of 50%.

See above for details of how Fuel Savings are achieved without affecting comfort.

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Initial or Factory Set Programmes

Do I need to decide what programmes I want when my DCD controller is first installed ?

No. The DCD Controller starts running with a set of programmes that is based on extensive user trials. It is recommended that new users should simply set the controller with the time of day and day of week, and leave it running with these programmes for a week in order to gain initial experience. The heating levels can of course be raised or lowered, on an ad hoc basis, during this time, and the programmes can then be adjusted in the light of the experience gained.

In practice, as the supplied set of programmes has been carefully researched in trials, it has been found that some 85% of users are content to run with these programmes on a permanent basis. Others modify the programmes slightly by adjusting the times and/or temperatures in the supplied programmes. In time, you may want to devise your own set of programmes - it is very easy to insert and delete programmes, as you wish - see Programming above.

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Brochure and Price Information

Where can I find this Information ?

See Latest Information for details of how to download our colour brochure, and for price and ordering information.


 

Contents

  Balancing of Central Heating
Base Area - Location
Boiler On/Off Cycling
Boiler Energy Managers and Optimisers
Boiler Types
BRE Tests - Importance
Brochure
Combi Boilers
Controller - Gravity Fed Hot Water
Controller - Location
Differentials - Temperature Switching
Energy Savings
Factory Set Programmes
Frost Thermostat
Fuel Savings
Fully Pumped System Valves
Gravity Fed Hot Water Control Valve
Gravity Fed Hot Water Installation
Hot Water Systems
House Temperature Uneven
Legionella Sterilization
Location - Controller
Location - Outside Sensor
Location - Room Sensor
Megaflow - Sensor Location
Minimum Heat Maintenance
Optimum Start
Outside Sensor - Location
Price and Ordering of a Controller
Programming - Legionella Sterilization
Programming Temperatures
Pump Control & Overrun
Room Sensor - Location
Savings without affecting Comfort
Savings in Fuel - 25% and much more
Savings on Maintenance
Sealed Hot Water Systems - Sensor

Smoothing of Central Heating Temperatures
Temperatures - Optimum Start
Temperatures - Programming
Temperatures - Central Heating Smoothing
Temperatures - Boiler On/Off Cycling
Temperatures - Switching Differentials
Temperatures - Central Heating Settings
Temperatures - Water Heating Settings
Temperatures - Legionella Sterilization
Temperatures - Outside Display
Thermostats - Usage and Types
Towel Rails
TRVs (Thermostatic Radiator Valves)
Underfloor Heating Zones
Underfloor Heating Valves
Unvented Hot Water Systems
Valves - Gravity Hot Water
Valves - Mid Position
Valves - Two Port
Valves - Underfloor Heating
Water Cylinder - Sensor Location
Weather Compensation
Zones - Parts of a House or Building
Zones - Upstairs & Downstairs
Zones - Underfloor Heating
Zones - What about more
   
  Sales and Technical Enquiries Return to Index (Home Page)




Last Updated in November 2008
©DCD Systems Limited 2008