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Wiring an OWL Intuition heating controller system for a thermal store By Steven Harris INDEPENDENT ENERGY EFFICIENCY AND RENEWABLE ENERGY ADVISOR m: e: w:
07958 99 22 92
[email protected] www.steven-harris.co.uk
Introduction This is a description of a way of setting up an OWL Intuition system for a Heat Bank thermal store where solar thermal is the primary heat source, followed by a solid fuel boiler stove. As neither of these sources can be controlled remotely, (i.e. you can’t make the sun shine or make a fire/strike matches remotely), it also gives control of a 3kW immersion heater that can be switched on remotely. This short description is primarily about the logic of installing the system. The use of the system and manual control buttons can be found in OWL instruction literature. The OWL Intuition system makes use of 240V AC wiring. As such, a suitably qualified person should carry out the installation work as there is a risk of fire and electrocution from incorrectly made installations. All power must be disconnected before undertaking any work. Smart amenity – what makes this system useful Thermostats and heating zones The system can currently operate up to four different space heating zones. These can be either be wired via traditional 240V AC wiring or wireless via RF. Traditionally wired thermostats tend to have triple and earth mains wiring. This provided neutral, live, switched live and earth to the thermostat. OWL thermostats however only required live and switched live as the thermostat itself and its relay is powered by replaceable AAA batteries. In a new build/installation it is always worth installing triple an earth as this gives spare wires for future technologies, however two core is all that is required for the OWL system. OWL thermostats have blind contacts to ‘park’ the neutral and earth wires found in traditional thermostat wiring. Using the thermostats and zones The advantage of the OWL system is that it allows easy intuitive, ‘full screen’ programming of temperature set points and heating programme/timing for each zone via an internet enabled computer. If the room(s) in the zone are below the required temperature in the required period the thermostat will close its relay connecting the live with the switched live.
At the other end of the wires At the under floor/radiator heating controller where the wires to the thermostats originates, the switched live wire becoming live will tell the controller to turn on the heating pump and open the appropriate zone value to allow hot water to flow into that zone. (A contact is also closed that in a traditional system can be wired to a gas boiler to ask it to come on). This is fine if there is heat available in the thermal store, but if there isn’t, or the heat left in it is being kept for DHW, it can result in the UFH circulating pointlessly or consuming heat reserved for DHW. For this reason the first of two OWL tank sensors is used. Tank Sensor 1 Tank sensors operate in the same way as room thermostats except they have a temperature sensor on a flying lead instead of hard wired within their body. This temperature sensor should be either installed in a spare sensor pocket in the thermal store around the same level as the UFH water take off, or fixed against the copper pipe of the UFH take off as close to the store as possible and securely wrapped in lagging and silver taped. This will mean the sensor will measure the temperature of the store at this point. Via an internet connected computer the temperature at which the tank sensor switches can be set and if required a time programme also set. This may be useful if you want to say, allow the tank to chill right down in the morning to allow harvest of low grade solar thermal heat yet reserve DHW in the afternoon for use in the evening. Linking the tank sensor to the heating circuit The power supply to the under floor heating/radiator controller should be wired via the normally closed (NC) contacts within the tank sensor. This will mean that when the tank goes below the set temperature and the tank sensor calls for heat, the power to the heating controller will be cut. Equally, once the store has achieved the set temperature, the tank sensor will stop asking for heat and the NC contacts will close again and allow the heating controller to operate if a zone thermostat is calling for heat. This all mean that if the store is cool and a zone thermostat ‘says’ its zone is cold and calls for heat, the tank sensor will ‘say’ back ‘sorry, you can’t have any cause I’ve got none!’ Wiring the immersion – Tank Sensor 2 Due to the high power connections involved, this job should be carried out by a suitably qualified person as incorrectly made connections can cause a fire risk. The OWL immersion controller is a completely independent system and is not interlinked with the zone thermostats or tank sensor 1. It allows the immersion to be programmed to make sure there is some heat in the store at different times on different days of the week.
The primary use of this is to make sure there is always enough heat in the store for morning showers. From experience this system gets most use in the Autumn and Spring when the boiler stove is no longer/isn’t yet being habitually lit for space heat and the solar harvest can be patchy or low powered. Generally the sensor is set to check if the store has heat for an hour before shower time, hence this may be a different time at weekends to weekdays. If the store is hot from the previous night’s fire or previous day’s solar harvest, the store will be up to temperature and the sensor will not ask the immersion to come on. Additionally since this sensor can be viewed and controlled via the OWL smart phone app, the immersion can be switched on from the phone away from the home. Useful if a store of hot water is needed for your return, and if the set point temperatures of tank sensor 1 and 2 are set appropriately, the immersion can even be used to heat the house. Installation of Tank sensor 2 The temperature sensor 2 is installed with its temperature sensor somewhere near the immersion heater. The exact location is not critical, but it should be either about level with it or slightly above. The tank sensor can only switch 8amps so is not capable of switching a 3kW immersion heater element by itself. For this reason a power relay is required. The tank sensor therefore switches the power relay actuator (switching side) on and off, which in turn switches the immersion power on and off (switched side). The immersion should be wired up via the power relay following the instruction supplied in its box using suitably power rated cable. • •
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A neutral bridging wire should be connected between the neutral input switched side terminal and the neutral switching side. The input live terminal should then be connected to the live of a two core cable and taken to the tank sensor and connected to the live terminal in the tank sensor. The other wire in the two core should be connected to the normally open terminal in the tank sensor. This wire will then become live when the tank sensor asks for heat. Back in the relay this (call for heat) wire should be connected to the switching live terminal. When the tank sensor thermostat calls for heat, the switched live wire will become live and energise the relay and therefore energise the immersion heater.
