{"id":281,"date":"2021-02-11T18:18:58","date_gmt":"2021-02-11T23:18:58","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/basichvac\/?post_type=chapter&p=281"},"modified":"2021-03-26T11:48:08","modified_gmt":"2021-03-26T15:48:08","slug":"low-voltage-thermostats","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/basichvac\/chapter\/low-voltage-thermostats\/","title":{"raw":"Low-Voltage Thermostats","rendered":"Low-Voltage Thermostats"},"content":{"raw":"Click play on the following audio player to listen along as you read this section.\r\n\r\nhttps:\/\/video.bccampus.ca\/id\/0_x8qb0i56?width=608&height=130&playerId=23448552\r\n\r\n[pb_glossary id=\"688\"]Low-voltage thermostats[\/pb_glossary]<\/strong> are smaller and cheaper to install and maintain, and the wiring does not need to have as high a voltage and power rating as their line-voltage counterparts. This is why [pb_glossary id=\"689\"]low-voltage control circuits[\/pb_glossary]<\/strong> are favoured for central heating units. Low voltage thermostats are also more sensitive to changes in heat than line-voltage thermostats, and so can provide more precise control.\r\n\r\nWhen controlling a single large heating unit, such as a [pb_glossary id=\"690\"]central gas furnace[\/pb_glossary]<\/strong> or [pb_glossary id=\"691\"]electric furnace[\/pb_glossary]<\/strong>, there is no zone control as with baseboard heaters; either the whole house is getting heated, or none of it is. A low-voltage thermostat installed in a central location, and powered by a [pb_glossary id=\"692\"]120 - 24V transformer[\/pb_glossary]<\/strong>, can senses the ambient temperature and be used to control a [pb_glossary id=\"693\"]relay<\/strong>[\/pb_glossary] to deliver power to the heating load.\r\n\r\nBy using an [pb_glossary id=\"447\"]extra-low-voltage[\/pb_glossary]<\/strong> source for the control circuit we get the benefit of lower cost and easier installation along with increased safety, allowing a simple two-wire low-voltage cable to be installed in an ideal location in the house. Because it is only meant to handle the control current and not the load current, low-voltage thermostats are highly responsive and can provide more accurate control than line-line voltage thermostats.\r\n\r\nSome models of low-voltage thermostats used to control central gas furnace or electric furnace loads incorporating heat exchanges and blowers, will have a small, series connected, resistive device called an [pb_glossary id=\"451\"]anticipator resistor[\/pb_glossary]<\/strong>. The purpose of this device is to fine tune the sensitivity of the thermostat and prevent overshoot of the desired room temperature.\r\n\r\nLow-voltage thermostats, fall into two general categories, some are simple temperature activated switches while others are more modern [pb_glossary id=\"694\"]electronic thermostats<\/strong>[\/pb_glossary] incorporating solid-state circuitry and allowing for programmable behaviours such as 24-hour cycles, and weekday vs weekend scheduling.\r\n\r\nElectronic thermostats use semiconductor components for both temperature sensing and control-circuit switching. If installed to replace an existing analogue thermostat, the electronic thermostat must have a separate power source, which is usually a battery.\r\n\r\n[caption id=\"attachment_312\" align=\"aligncenter\" width=\"350\"]\"An An example of a programmable thermostat.[\/caption]","rendered":"

Click play on the following audio player to listen along as you read this section.<\/p>\n

https:\/\/video.bccampus.ca\/id\/0_x8qb0i56?width=608&height=130&playerId=23448552<\/p>\n

Low-voltage thermostats<\/a><\/strong> are smaller and cheaper to install and maintain, and the wiring does not need to have as high a voltage and power rating as their line-voltage counterparts. This is why low-voltage control circuits<\/a><\/strong> are favoured for central heating units. Low voltage thermostats are also more sensitive to changes in heat than line-voltage thermostats, and so can provide more precise control.<\/p>\n

When controlling a single large heating unit, such as a central gas furnace<\/a><\/strong> or electric furnace<\/a><\/strong>, there is no zone control as with baseboard heaters; either the whole house is getting heated, or none of it is. A low-voltage thermostat installed in a central location, and powered by a 120 - 24V transformer<\/a><\/strong>, can senses the ambient temperature and be used to control a relay<\/strong><\/a> to deliver power to the heating load.<\/p>\n

By using an extra-low-voltage<\/a><\/strong> source for the control circuit we get the benefit of lower cost and easier installation along with increased safety, allowing a simple two-wire low-voltage cable to be installed in an ideal location in the house. Because it is only meant to handle the control current and not the load current, low-voltage thermostats are highly responsive and can provide more accurate control than line-line voltage thermostats.<\/p>\n

Some models of low-voltage thermostats used to control central gas furnace or electric furnace loads incorporating heat exchanges and blowers, will have a small, series connected, resistive device called an anticipator resistor<\/a><\/strong>. The purpose of this device is to fine tune the sensitivity of the thermostat and prevent overshoot of the desired room temperature.<\/p>\n

Low-voltage thermostats, fall into two general categories, some are simple temperature activated switches while others are more modern electronic thermostats<\/strong><\/a> incorporating solid-state circuitry and allowing for programmable behaviours such as 24-hour cycles, and weekday vs weekend scheduling.<\/p>\n

Electronic thermostats use semiconductor components for both temperature sensing and control-circuit switching. If installed to replace an existing analogue thermostat, the electronic thermostat must have a separate power source, which is usually a battery.<\/p>\n

\"An
An example of a programmable thermostat.<\/figcaption><\/figure>\n
definition<\/span>