The DCD Heating Controller

Picture of Controller

Comfort and Convenience
is put first
Users may expect an annual
saving of at least 25% on fuel consumption
A proven track record
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Contents

BRE Investigation
Central Heating Temperature Variation
Clock Operation
Delayed Switch-On Period
Delayed Water Valve Closure
Description - General
Features
Frost Protection
Heat Maintenance - Minimum
Hot Water Temperature Variation
Industrial and Other Applications
Installation - Simple & Straightforward


Memory Protection
Operation - Simple to Use
Optimum Start (Time Heat Required)
Outside Temperature
Override for Heating and Water
Programmes for Heating and Water
Pump and Valve Exercise
Pump Overrun
Size - Physical Dimensions
Smoothing of Central Heating
Water Boost
Wiring and Cabling
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Building Research Establishment Investigation

Summary of Findings

The DCD Domestic Heating Controller has been investigated by the Building Research Establishment, an Executive Agency of the Department of the Environment, and it is with their permission that the Overall Summary of their findings is reproduced below.

The DCD heating controller is a purpose built full featured unit aimed at the domestic housing market for the control of central heating and hot water. It offers ten discrete heating programmes for each day of the week for central heating and hot water, together with additional features such as optimum start, temperature smoothing, boiler cycling control and pump overrun.

In the simplest type of installation, the controller may be used to replace a time clock but, at BRE, a house was set up with a full installation comprising; the main controller, and sensors for room, hot water and external temperature. The investigations were carried out in two traditionally constructed detached houses, built with insulation standard just beyond current building regulations and equipped with modern well controlled heating systems. Both houses were equipped with simulated occupancy, which is programmed to provide the incidental gains from a "four person" household. The main points that emerged from the investigations were:

The tests demonstrated that the DCD controller is a capable unit with the ability to manage domestic heating and hot water services to a high standard and provide substantial energy savings. It has many features and can accommodate a wide range of user options in both installation and operation. Reducing temperature will always save energy but, with the flexibility of the DCD controller, warmth can always be provided when it is required. Bottom line cost saving will depend upon the way the user wants to run their heating system but, with the DCD controller, features such as optimum start, temperature smoothing and pump overrun can offer improved system management whatever the desired temperature requirements.

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Features

General Description

The controller offers up to ten discrete heating programmes a day for each day of week, for water and for central heating, with optimum start and central heating temperature smoothing. It therefore provides great flexibility in programming requirements for maximum comfort at minimum fuel cost, and avoids the overheating of rooms beyond the temperature required.

The controller comes supplied with a room sensor, a water sensor and an outside sensor to provide the full benefits of its facilities. It may be unpacked from its box, connected up and, after setting the correct day of week and time, left running with standard factory set heating programmes. It builds up its history of operating experience, on a daily basis, which it uses to progressively improve its heating optimisation performance.

Once the controller is in operation, easily identified keys enable the majority of requirements for temporary changes to be made. The Boost key provides water heating to order, at times when no water heating programme is in operation, the Heating Programme Override key provides manual control of central heating when needed, and further keys allow temporary programme changes to be made for time and temperature. Naturally, once initial experience has been gained, the user may enter his own heating programmes and temperature settings in place of the factory settings.

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Simple to Use and Operate
The diagram of the front panel illustrates the straightforward design with the simple and easy to use controls.

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Control Panel




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Simple for the Installer

Besides being simple to use from the point of view of the user, the Controller is simple to install. Note that there is no crossover wiring and that the connections for the sensors may be made with low voltage cabling, such as bell wire or telephone cable.

Direct connections may be made when separate central heating and water control valves are installed, also when two pumps (including dual pumps) are used.


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Connections to Terminals on Base



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further details, and other layouts

Standard Programmes for Central Heating and Water Heating

The controller allows for a maximum of ten programmes to be set for each day of the week, making a total of seventy programmes in all. Each programme may contain different settings for central heating and for water heating and each will optimise separately.

The initial optimum start values are set at thirty-five minutes for heating and forty-five minutes for water. The values are progressively modified after the first day's operating, on a self-learning basis; an important exception is that records are not updated when an Override is operated, so the controller will be slower to learn requirements if Overrides are frequently used in the early days of a new installation.

On installation, the Controller should be set with the day of week and the current time, then left running with the factory set heating programmes. These programmes have been developed and tested in user trials and it has been found that some 85% of users are content to run their heating systems without making changes. Users are therefore advised to run with the factory set programmes, in order to gain initial experience, making only ad hoc Override adjustments to find the temperature settings that they find most comfortable; with one or two exceptions, that are described in the operating instructions, they are advised against changing the standard programmes during the first week or so.

The standard programmes vary the central heating and water temperatures, according to the time of day, thus ensuring that comfortable levels are maintained and waste is avoided by not running heating when it is not needed. A feature of the standard programmes is the overnight heating programme with a low temperature setting that is set to ensure that a satisfactory minimum level is maintained, whatever the weather; the cost of this heating is normally offset by a saving in the first or "wake up" programme of the day as it only operates in very cold weather. The overnight programme has been found to be especially beneficial for elderly people, those with small children, sufferers of Angina, Asthma, Bronchitis, etc.

The controller may be reset to the original factory installed configuration and heating programmes. This may be necessary if major changes are made to the heating installation or the controller is moved to another building. The facility to reset the whole controller with the factory installed configuration is different from and should not be confused with the heating programme reset that forms part of the Override facilities.

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Optimum Start (Time Heat Required)

An optimum start facility that enables the user to set the time and temperature that heat is required for central heating, or for hot water, is quite different from the conventional setting of time clocks for on and off times. It offers significant advantages in terms of convenience and comfort, as well as enabling substantial energy savings over time clock systems which switch on and off the heating mechanism at a standard preset time, whatever the weather conditions happen to be. It ensures that heat is provided when required, yet avoids waste incurred by switching on too early on warmer days, by relieving the user of guesswork and allows him simply to set the system with details of the heating temperature needed and when the temperature specified is required.



Chart showing operation of Optimum Start
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Furthermore, when a central heating or water heating programme is followed by another programme with a higher temperature, the currently running programme may be cancelled automatically to allow the later programme to start early to warm up to the higher temperature when conditions make this desirable. Thus, for example, an evening programme that runs to 6.30 p.m. at 19C, that is followed by a programme that requires a temperature of 21C, may be superseded by the later programme at 6 p.m., or whatever earlier time may be appropriate for the prevailing weather temperature conditions, in order to raise the temperature to 21C by 7 p.m.

The DCD designed system employs a method of progressive updating of heating history data based on actual performance, with approximately six thousand cells of stored information. The history is used to predict independent warm up times for both water and central heating, for each set heating programme, according to stored data for the nearest similar prevailing weather and heating conditions. Optimum start normally offers the greatest benefit when a house is warmed up first thing in the morning and the chart, reproduced above, shows the effect on three consecutive Winter days that were taken at random. It will be appreciated that a standard time clock system, or one based on a simple optimising algorithm, without regard to water heating requirements, could not match the performance of the DCD optimum start system in the three days illustrated.

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Smoothing of Central Heating

With a conventional domestic heating system, heating cycles involve heating radiators from a relatively low temperature and then switching the heating off when the room thermostat reaches a set temperature. The radiators effectively hold a reservoir of heat when the room thermostat reaches temperature and, after the heating is switched off, the room temperature continues to rise as this heat is dissipated by the radiators.

With the smoothing system, operational experience is recorded and used to adjust and smooth out heating cycles. This offers advantages in terms of greater comfort by avoiding fluctuations in temperature, and in terms of savings in energy, by smoothing or evening out peaks when rooms would otherwise be heated beyond the temperature that is needed for comfort. Furthermore, while boiler cycling is regulated to obtain fuel economies and to minimise maintenance costs, the controller does not restrict boiler output in order to obtain fuel economies at times when the full power of the boiler is needed to maintain maximum comfort.

An appreciation of the benefits of the DCD Smoothing System will be found in the summary of the report by the Building Research Establishment.

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Central Heating Temperature Variation

A facility to vary temperatures at different times in the day offers a number of advantages.

For example, a greater degree of comfort may be obtained by raising the central heating temperature in the evening when people are sitting down, even though it may have been switched on all day at a background temperature level. It becomes possible to save fuel by running central heating at a lower temperature during the main part of the day in most homes.

Heating programmes in the controller may be individually set with different temperatures to cater for varying needs. These may include setback or overnight temperature settings, and settings aimed at saving fuel on days or parts of days when a house is not occupied.

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Hot Water Temperature Variation

A facility is provided to allow variable hot water temperature control in conjunction with a hot water temperature sensor.

In operation, for example, the hot water temperature may be programmed to provide at least one good bath but, to cater for peak times in a family, it may be an advantage to raise the temperature for an hour or so at some time in the day when two or more baths may be drawn in reasonably quick succession or simultaneously.

It is uncomfortable and unwise to keep water at too high a temperature. It can also be a nuisance and costly in hard water areas, where showers and thermostatic mixer control valves can accumulate scale more quickly and thus need to be serviced at frequent intervals. Furthermore, the facility to operate water heating at the temperature at which it is required, and avoid heating it all day at the maximum temperature needed for peak times, results in a dramatic reduction of boiler running time solely for water heating temperature maintenance.

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Water Boost

In a system where a cylinder thermostat or sensor is fitted, pressing a button on the controller brings the hot water up to temperature, when a water heating programme is not currently running. The temperature may be adjusted when a Boost is in operation, any adjusted temperature will be retained in the controller's memory and used the next time that a Boost is required.

The user may also use the Boost button to restore hot water to its full set temperature after, for example, drawing off a bath, when there is a currently running water heating programme that is due to finish before this can be done. Besides entry by button, a Boost can be set in a stored heating programme to automatically extend the programme, when necessary, each time it is run, to bring the hot water to temperature before it switches off.

A Boost that is running or which is due to come into operation at the end of the current programme, may be cancelled by depressing the Boost button, no matter whether it was initiated by a stored programme or by button.

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Override for Heating and Water

Override facilities are extremely valuable for dealing with variations in the habits of a household as they enable temporary changes to be entered without the need to amend a previously stored heating programme. Whenever any of the facilities are in operation, the word "Override" appears on the display. The facilities allow:

Finally, a reset button is provided to cancel any overrides entered and restore the controller to normal operation under programme control, at any time.

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Delayed Switch-On Period

This facility permits temporary suspension of central heating and water heating programmes for a period of time, entered by the user, with automatic return to programmed operation at the end of the period of time entered.

Therefore, it is possible to switch off heating for holiday periods and other absences from home, and to have full operation of heating programmes restored automatically in accordance with the delay criteria.

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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 each period of heat demand. There are two main reasons why this is done:

Pump overrun is an integral part of the DCD temperature smoothing procedure (see above) which maintains temperature to within 0.1°C of the temperature required. It provides a minimum of one minute of pump overrun after the boiler is switched off at the end of each period of demand. Bearing in mind that a typical modern boiler may contain only a couple of litres of water, which may be changed every few seconds, a one minute pump overrun should be more than enough to meet boiler manufacturers’ requirements for boiler safety.

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Delayed Water Valve Closure

It is advantageous to include a motorised valve in gravity feed hot water systems, to control water temperature by programme in conjunction with a thermostat or temperature sensor. The arrangement allows the boiler to be run at a high temperature setting, regardless of the hot water temperature required, so that the higher temperature makes it possible to heat up both central heating and hot water quickly and efficiently when needed.

A drawback to the use of a motorised valve in a standard system is that residual heat in the boiler cannot be used at the end of a heating programme, or when the set temperature is reached, and the valve is allowed to close automatically. The controller overcomes this difficulty by keeping the valve open for a period after water heating is completed, when there is no demand for central heating to utilise the residual heat in the boiler.

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Pump and Valve Exercise

This facility runs the pump for a period of five minutes before the start of the first water heating period in the day, whenever it has not been run during the previous seven days. This is done to protect the pump and ensure that the build-up of sediment does not overload the starting torque of the pump, in summer months, in systems with gravity hot water circulation and pumped central heating.

The exercise facility also operates valves to prevent them from sticking when they are not used for long periods.

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Minimum Heat Maintenance

It is possible to detect whether the surrounding temperature drops below a preset level - this is factory set at 12C. 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.

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Frost Protection

This enables a controller to be linked to a thermostat located near to a boiler sited in an exposed position (e.g. a garage).

Whenever 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.

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Outside Temperature

Where an external sensor is installed, the outside temperature is displayed by the controller on depression of the appropriate button. When this is done, the outside temperature is displayed for ten seconds and the controller then returns to it's normal display.

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Memory Protection and Clock Operation

All settings, heating programmes, optimum start history and clock operation are maintained by an internal self-charging battery that automatically comes into operation whenever the mains supply is interrupted. When fully charged, the battery will support these functions for several months.

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Size - Physical Dimensions

Dimensions : 215mm x 130mm x 85mm..

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Applications

The Controller can be used for time clock replacement in basic heating systems with gravity hot water and pumped central heating, fully pumped systems with two valves or with a diverter valve, systems with combination boilers, condensing boilers, oil fired boilers, LPG boilers, etc. Version for heating swimming pools, including pool water and pool hall air temperature, etc.

The controller can also be linked to other controllers to control the heating of zones in larger houses, offices, etc.



Contents

  BRE Investigation
Central Heating Temperature Variation
Clock Operation
Delayed Switch-On Period
Delayed Water Valve Closure
Description - General
Features
Frost Protection
Heat Maintenance - Minimum
Hot Water Temperature Variation
Industrial and Other Applications
Installation - Simple & Straightforward


Memory Protection
Operation - Simple to Use
Optimum Start (Time Heat Required)
Outside Temperature
Override for Heating and Water
Programmes for Heating and Water
Pump and Valve Exercise
Pump Overrun
Size - Physical Dimensions
Smoothing of Central Heating
Water Boost
Wiring and Cabling
  Go to DCD Site Index (Home Page)
 




Last Updated in November 2008
©DCD Systems Limited 2008