In Canada, an estimated 81% of household energy use is for space heating & domestic hot water generation1. In the US, estimates place this at 61%2. This presents a remarkable energy savings opportunity.
In order to provide comfortable indoor temperatures, the rate of heat supplied to a building must equal the rate of heat loss. The greatest factor affecting how much heat a building requires is the outdoor temperature. Even in a well-insulated building, heat loss increases as the outdoor temperature falls.
Traditional heating systems do not know if it’s a cool autumn night or the coldest winter day. Because of this, the boiler always operates at a temperature calculated to make up for heat loss on the coldest day of the year. This is called the ‘design’ temperature. On average, this extreme temperature is needed for less than 10 days in a year.
Outdoor Temperature Reset saves energy with modern condensing boilers as well as older non-condensing models. For a worry free installation, look at controls that include both Outdoor Temperature Reset as well as Indoor Temperature Feedback. By combining these two features, the system provides maximum energy savings and comfort.
Outdoor Temperature Reset with Indoor Temperature Feedback ensures modern high efficiency condensing boilers are operated using the lowest possible water temperatures. This is important because the efficiency of these boilers increases with lower return water temperatures.
The chart on the left illustrates how the efficiency level of a condensing boiler decreases as the return water temperature increases. The performance advantage of these boilers can be lost if they are not given the chance to operate at lower temperatures.
Indoor Temperature feedback improves on Outdoor Temperature Reset control by reacting to heat loss or gains caused by people, appliances, the sun, wind or any other factor besides the outdoor temperature. Communication with tekmarNet® thermostats enables tekmarNet® controls to adjust system water temperatures based on both outdoor and indoor temperatures. With Indoor Temperature Feedback, contractors no longer need to return to the site to fine tune control settings if the anticipated design temperatures were too low. In tekmarNet® systems, the control automatically takes care of shifting the heating curve to prevent overheating or underheating.
A study conducted by the MCEE found a range of savings from 5 to 25% when apartments with older boilers were retrofitted with Outdoor Temperature Reset and automatic Warm Weather Shut Down control. Expected savings differ with building construction, system components, building use and outdoor temperature range.
Download the study
Boilers of all kinds, heat pumps and even mixing devices can be controlled to provide Outdoor Temperature Reset to a system. Contractors can make use of existing thermostats or improve the system performance further by selecting a tekmarNet® communicating thermostat and system control combination. Indoor Temperature Feedback is a feature provided by tekmarNet® communication.
If the boiler is used to generate domestic hot water, the tekmar control will temporarily operate the boiler at a higher temperature when the domestic tank requires heat. Once the tank target is satisfied, the control will lower the boiler temperature as required by Outdoor Temperature Reset.
With Outdoor Temperature Reset, energy will be saved whenever the outdoor temperature is above design temperature and space heating is required. When you add Indoor Temperature Feedback, energy will also be saved when heat is added to the building by people, appliances or the sun.
The coldest average outdoor temperature specific to your location is referred to as the ‘design’ temperature. Heating system installers use this number to determine how much heat will be required to keep the building warm enough on the coldest days of the year.
HVAC system controls including house, boiler, steam, universal, and mixing controls.
tekmarNet® HVAC system controls provide Indoor Temperature Feedback when used in a system with tekmarNet® Thermostats.
Installers should start by considering the number and type of heat sources in the system. If the system provides domestic hot water, multiple water temperatures or cooling, a control that supports those features is required. Comparison charts are provided on this website to help.
Contractor Magazine article about Outdoor Temperature Reset by Carol Fey
In-depth information about thermal comfort Healthyheating.com