DIY heating plumbing tips 3 an explanation of residential heating and hot water controls.
Effective heating and hot water controls will increase the operating efficiency of your heating system.
Installing good effective controls will reduce your energy consumption by giving you greater flexibility in system management over temperature and heating periods.
On this page you will find sections on:
A time switch offers a simple 'on- off' control over one circuit. It is particularly suited with a combination boiler as 'hot water on demand' is the default setting for the boiler - you only need a time switch for the space heating side.
Choose one that is easy to understand and install it in a location where you can easily read and alter it.
A programmer does more than a time switch, it can switch two circuits (separately) and there are three basic types.
Choose one that is easy to understand and install it in a location where you can easily read and alter it.
A room thermostat is a simple temperature control device that monitors the air temperature designed to give you control over your desired temperature level for your house by starting up the boiler and pump when the room temperature falls below your set level.
Most room thermostats include an 'anticipator' - basically this smooths out the temperature cycle so the on and off periods are not too long.
The room thermostat should be installed ideally in an area regularly heated where there is free air circulation such as a hallway, and away from any heat source including direct sunlight. Remember a room thermostat controls the boiler's space heating function for the entire house.
If installed in rooms then these rooms should be without any other supplementary heating that will affect the room thermostat's sensor (e.g, gas fires, electric fires and open fires). There must not be a thermostatic radiator valve (TRV) attached to any radiator in the same room as the room or programmable room thermostat.
For individual room control install a thermostatic radiator valve (TRV) so enabling you to have individual room temperatures - see below for more information on TRVs.
These thermostats are generally installed 1.5 meters above the floor (or 1 meter for people in wheelchairs).
A programmable room thermostat offers you greater flexibility over time and temperature settings than a standard room thermostat. Programmable room thermostats are capable of 24 - 7 control for both your heating and domestic/residential hot water.
Some models have a night setback feature, the setback feature keeps the heating system on at nights but reduces the room temperature by about 3°C. This feature is mainly used with underfloor heating as it has a slow response in both heating and cooling.
A cylinder thermostat sets and monitors temperature for stored hot water. In 'open' vented cylinders they are usually strapped to the side. In unvented cylinders they are already factory installed (some unvented cylinders have temperature probes inserted during installation). Cylinder thermostats are attached at 1/3 of the cylinder's height from it's base, and are used with a motorized valve for control over the water temperature.
A Frost thermostat is an air thermostat designed to maintain a minimum temperature to prevent damage to pipework, boiler and house. It should be fitted in a suitable unheated area such as a garage.
When boilers are installed in unheated areas like a garage then a pipe thermostat should be fitted to the pipework in that area to prevent the boiler from firing and wasting fuel unnecessarily in cold weather.
Thermostatic radiator valves (TRV's) provide an upper temperature limit to individual rooms. They can prevent overheating in a room from solar gain and incidental gain from other appliances or increased people activity.
TRV's do not control the boiler and therefore offer no real energy saving, even when the boiler is not 'interlocked'. Once interlocked the boiler will only fire (start) when there is a 'call' (demand) from the room thermostat, or cylinder thermostat if using a hot water storage cylinder.
TRV's are useful in public buildings, schools, hospitals, and nursing homes etc
Thermostatic radiator valves should not be in the same room as the room thermostat. If more than half of your radiators are fitted with TRV's then an automatic bypass valve will be necessary (more on automatic bypass valves further down the page)
A thermostatic hot water temperature limit valve is an additional safety valve designed to limit the hot water temperature in stored hot water cylinders, and they are self acting (without a motor).
These are units that sense the primary water temperature and a separate remote sensor that detects the stored water temperature. They should have a electrical switch to provide 'boiler interlock' (more on boiler interlock further down the page).
The most common domestic/residential motorized valves are the:
The 3-port valve provides a separate circuit for heating and hot water - not both together. The 3-port 'mid-position' valve however, allows the heating and hot water circuits to be open at the same time by sharing the water flow.
The 2-port valve only provides one circuit, heating or hot water.
A hot water and one heating zone using one 3-port or one 3-port mid position valve is called a Y-plan. A hot water and one heating zone using one 2-port valve for hot water and one 2-port valve for heating, is called an 'S-plan'.
For an additional heating zone (homes with a floor area larger than 150m2) use a separate 2-port valve and room timer, this is called an 'S-plan plus'.
Motorized valves basically open or close off a pipe circuit. They should not be positioned in-line (within) the open safety vent pipe or feed and expansion pipe nor should any other valve for boiler safety.
A boiler interlock is just simply a wiring arrangement to prevent the boiler from firing when there really is no demand for heat for space heating or hot water (the boiler's internal thermostat thinks it should fire because the temperature has fallen internally - this is called boiler cycling).
A boiler is interlocked when it is only switched on or off when there is a call from the room or programmable room thermostat, or from the hot water cylinder thermostat, or by a boiler manager system (a built-in control).
For regular/conventional boilers the system is interlocked so that the room or cylinder thermostat switches the boiler and pump on through the motorized valve. Combination boilers need only to be interlocked by the room thermostat.
The automatic bypass valve is used to maintain and control a minimum water flow rate through the boiler and to limit any increased circulation pressure when radiators are closed by thermostatic radiator valves (TRV"s) or manually.
An automatic bypass is better than a fixed (manually fixed) bypass and is important if most of the radiators have TRV's, because when most TRV's are open then the automatic bypass stays closed allowing full water flow through the system.
When the TRV's start to close the automatic bypass starts to open so maintaining the flow rate through the boiler. Most new system boilers include an automatic bypass within the boiler unit.
With a fixed bypass there is always a constant flow of hot water directly into the boiler primary return pipe causing the boiler to operate at a higher temperature which reduces the efficiency of the boiler's heat transfer.
Note: A bypass circuit must be provided if the boiler manufacturer specifies it.
A boiler energy manager generally controls a number of functions that usually include a weather compensator, optimum start, frost protection, night setback, self adaptive function, anti-cycling and hot water control.
Boiler energy managers are designed to improve efficiency, protect the boiler and to reduce running costs.
Weather compensators improve the efficiency of boilers by monitoring internal and external temperatures. As the external temperature rises the boilers water temperature is reduced adjusting to the external heat gain, and vice versa when the external temperature falls.
Note: External sensor should be located on the non-sun side of the house so it isn't in direct sunlight.
The delayed start feature is associated with the external and internal temperature sensors, delaying the start time of a boiler when the weather is mild, thereby saving energy.
Optimum start will enable pre-set design temperatures to be achieved at a chosen time by adjusting the heating start time (this compensation is made due to the external temperature).
Night setback enables heating during the night at a lower temperature, particularly useful with underfloor heating systems as it reduces the systems warm up time.
Night setback can be achieved with a programmable room thermostat as different heating levels and times can be set as it is a 24hr - 7day programmer.
This feature learns previous temperature settings (characteristics) so it can reduce the boiler's running time (optimizing the boiler to your heating patterns) thereby saving energy.
The anti cycling control is designed to reduce the cycling frequency of the boiler by delaying the start. However, independently this boiler feature doesn't offer any real energy savings - to achieve energy savings the boiler should be interlocked so it only fires when there is a demand for hot water or space heating.
Most modern solid fuel boilers are thermostatically controlled to vary the amount of air to the fire which adjusts the burn rate. A time switch, room or programmable room thermostat can be used to operate the circulator pump for internal temperature control.
However, with solid fuel boilers the combustion isn't really stopped so for safety reasons there must be a 'heat-sink' or 'heat bleed', e.g, a gravity fed radiator or hot water cylinder that is connected to the system - independent of any controls.
Thermostatic radiator valves (TRV's) can be used with solid fuel boilers, however, at least two radiators should not have TRV's to prevent boiling in the system by acting like a heat-sink, and ideally located in the center of the house thereby putting the heat to good use.
Hydronic (wet) systems
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