tekmar Glossary

In systems where tenants have control of the space temperature, a central zone control with a temperature Adjustment Range Limit can allow the building owner to limit the maximum space temperature in the zones. This function saves energy by limiting the heat supply to the zones.

In most hydronic systems there are several heating zones within one cooling zone. Until now, unfortunately, the cooling system was not integrated with the heating system so there were conflicts between the heating and cooling operation. tekmarNet®4 communication allows the heating zones to be associated to the cooling zone. Cooling and heating operation can now be integrated in order to prevent simultaneous heating and cooling within the same zone.

In order to decrease temperature swings and increase boiler efficiency, this function automatically changes the on / off differential of the boiler based on the heating load. As the load increases, the differential will decrease to minimize temperature swings. As the load decreases, the differential will increase to prevent short cycling.

When multiple controls in a single system try to operate the boiler(s) simultaneously, short cycling can occur. For the most efficient boiler operation, only one control should operate the boiler(s). All of the remaining controls should send a simple on / off signal to the boiler control. This function when used with a proper boiler control improves the system operation by preventing short cycling of the boiler(s). This also allows for easy integration of controls into existing systems.

Many systems, such as radiant heating, use a mixing device to reduce the system supply water temperature. The boiler in these systems should be operated at the minimum allowable water temperature in order to reduce standby losses. As the heating load increases and the mixing device is fully open, the boiler temperature should be increased to satisfy the heat requirement. This function provides higher system efficiencies and better controllability by operating the boiler at the proper temperature.

The heat up and cool down rate of a boiler depends on how much thermal mass the boiler contains. By knowing how fast the boiler heats up and cools down, the control can more accurately determine the required number of stages to turn on. The Boiler Mass function allows the multiple boiler control to intelligently stage the boiler plant. This function increases the efficiency of the system by reducing unnecessary staging.

Most boilers require a minimum supply water temperature in order to prevent corrosion from flue gas condensation. The control should therefore only modulate the boiler supply water temperature down to the boiler manufacturer’s minimum recommended operating temperature. This function allows the user to adjust the boiler minimum supply temperature based on the type of boiler being used.

A boiler is controlled by turning it on and off. In applications where outdoor reset is used, the boiler temperature can be lowered based on the outdoor temperature. Resetting the boiler temperature is limited by the boiler manufacturer’s minimum recommended operating temperature and allows water temperature reset for about 50% of the heating season. This function improves comfort by supplying the right amount of heat, and provides higher energy savings by minimizing distribution and boiler standby heat losses.

When a boiler is turned off some heat remains in the mass of the boiler. If the flow through the boiler is stopped at the same time the boiler is shut off, the residual heat is lost. Therefore, after operation of the boiler the residual heat in the boiler should be purged to the system in order to decrease standby losses. This is accomplished by turning the boiler off but keeping the system pump on for a period of time. This function increases system efficiency by minimizing standby losses.

To protect the boiler against flue gas condensation and thermal shock, a mixing device should be used to control the load on the boiler. If the temperature of the boiler is below the condensation temperature or the return water temperature suddenly cools down, the mixing device can back off, allowing the boiler loop to come up to temperature. By protecting the boiler, this function provides longer boiler life.

When combining setback with outdoor reset, the morning recovery period can be extremely long. By increasing the supply water temperature after the end of the setback period, a faster pick-up can be achieved. This allows for longer setback periods and therefore more energy savings can be obtained.

A characterized heating curve is a more accurate method of outdoor reset. Each type of terminal unit delivers heat into a building with different proportions of radiation, natural convection and forced convection. With a characterized heating curve, the control takes into account both the outdoor temperature and the type of terminal unit in order to determine the best water temperature for the system.

At extreme cold outdoor temperature, considerable energy can be saved by turning the snow melting system off. With these extreme outdoor conditions, the snow may only be partially melted resulting in ice formation and a safety hazard. Cold weather cutoff (CWCO) prevents the system from turning on if there is insufficient capacity to fully melt the snow

Most indirect fired DHW tanks require a boiler supply water temperature of at least 180°F (82°C) in order to transfer sufficient heat. If the boiler is also using a reset control for space heating, the water temperature may be below the temperature required for DHW operation due to the current heating curve or WWSD setting. Therefore the control must override the outdoor reset and increase the boiler temperature. This function allows for shorter DHW tank recovery times.

When DHW priority is used, the water temperature within the heating terminals may have cooled down significantly lower than the boiler operating temperature. When the DHW operation is complete the DHW pump will turn off and the system pump may turn on. This could cause a large temperature drop in the boiler return water, and therefore, may induce thermal shock. In order to provide a smooth transition between the DHW and heating loads the control briefly operates the two pumps simultaneously in order to mix the two returning water temperatures.

To ensure that the DHW tank is up to temperature after the DHW Setback period the control must raise the tank temperature before the setback period ends. This can be accomplished automatically by using a control that has an optimum start / stop function. This function increases comfort by ensuring the DHW tank is up to temperature at the beginning of the occupied period.

During DHW operation, the boiler temperature is normally raised above 180°F (82°C). Once the DHW tank is satisfied, the residual heat from the boiler may be wasted if there is no other call for heating. This residual heat from the boiler should be purged in order to reduce standby losses. This is accomplished by turning the boiler off but keeping the DHW pump or valve operating for a purging period. This function increases system efficiency by decreasing boiler losses.

DHW priority allows the DHW tank to recover faster by temporarily suspending the heat supply to the heating system. All of the available heat is provided to the DHW tank for a period of time. This function provides more comfort by ensuring faster DHW pick up times and increases system efficiency by often allowing the use of a smaller heat source.

If DHW priority is selected then heat to the heating system is stopped during a call for DHW. At cold outdoor temperatures the building may freeze up when there is a long call for DHW. In order to prevent this, the control must be able to override the priority and simultaneously operate the heating system and the DHW. The maximum time allowed for DHW priority should decrease as the outdoor temperature drops. This function provides more comfort by preventing large temperature drops in the space during DHW operation.

During the night, or when people are not within the building, energy can be saved by lowering the DHW tank temperature. This is achieved by ignoring the DHW call for heat during the setback period. Energy savings is obtained through lower heat losses from the tank as well as by preventing inefficient boiler operation during periods of low DHW demand.

This function rotates the firing sequence of a group of staged boilers based on the accumulated running hours of each stage. When one stage has accumulated 48 hours more running time than any other stage, the operating sequence is rotated. The stage with the least running hours is rotated in the firing sequence to turn on first, while the one with the most running hours will be last. This function increases the quality and reliability of the boiler plant by ensuring equal running times of all boilers.

The control operates the system components every three days for a few seconds to help prevent corrosion build up and the subsequent seizure. The control must ensure that during exercising no heat is supplied to the zones in order to prevent overheating in the summer.

Most boilers have built in safety delays before the burner is allowed to fire. The fire delay function allows a boiler staging control to account for the delay between the time that the control signals the boiler to operate and the burner actually fires. By taking into account the delay time, the control can more accurately determine the required number of stages to turn on. This function improves the efficiency of the system by minimizing short cycling in a multiple boiler system.

When multiple boilers are staged and rotated, the last stage can be fixed to fire last. A common application is to allow a second boiler plant, such as a DHW boiler plant, to assist with the heating when the DHW system is satisfied. Another common application is to front end load an older inefficient boiler with several higher efficiency boilers. Most of the heating load can be satisfied by the higher efficiency boilers and only during extreme conditions will the old boiler be allowed to fire. This function allows for added flexibility when designing or retrofitting a boiler plant.

When multiple boilers are staged and rotated the first boiler can be fixed to be fired first at all times. This function allows the boiler nearest to the chimney to create sufficient draft to prime the chimney. This function can also be used to increase boiler plant efficiency by selecting a high efficiency boiler to be cycled first. This higher efficiency boiler takes the part load of the boiler plant which increases overall efficiency.

Floating action is an output used to modulate the position of an actuating motor and mixing valve. Floating action either provides power to drive the motor further open or closed. If no power is supplied, the actuating motor remains at its present position. This is a simple and cost effective method for controlling the position of a mixing valve.

In radiant systems it is common to hear the complaint that the floors are cold. However, one must consider that the floor may feel cold, but the room target temperature is satisfied. A slab sensor allows the homeowner to select a minimum temperature in the slab for comfort reasons. The minimum floor temperatures can be automatically changed based on the setback schedule selected. The installer may also select a maximum floor temperature in order to protect floor coverings.

Heating and cooling interlock prevents the system from heating and cooling simultaneously. When the heating room temperature units (RTU) have been satisfied for a period of time, the control allows for the cooling unit to operate. If a cooling RTU is used, the control operates the cooling unit to maintain space temperature. This function simplifies external wiring, and prevents inefficient system operation.

Most buildings have internal heat gains and losses due to people, passive solar heating, or opening of doors. If only the outdoor temperature is measured, the control cannot compensate for these heat gains/losses and overheating or under-heating may occur. Indoor temperature feedback prevents this by shifting the heating curve up or down, in order to fine adjust the supply water temperature to the heating terminals. Single or multiple tekmar indoor sensors or room temperature units (RTU) are required to provide the feedback to the Reset Controls. This function provides more comfort by preventing overheating or under-heating.

Many boilers or water heaters have two stage burners. The control must therefore stage the operation of the burner by first firing the lo fire and then the hi fire. If equal run time rotation is desired, the control must now rotate the two stages in sets of two. This ensures that the burner always fires in the proper sequence while still ensuring equal running times of all boilers.

In order to increase the efficiency of a steam system, a Lockout or cool down period before each heating cycle can be used. The lockout differential ensures that the condensate temperature drops before turning the boiler on for the next cycle. This increases the efficiency of the system by removing the latent heat from the steam remaining in the heating system after the boiler shuts down.

The full range of temperatures required through a heating season can be provided with a non-condensing boiler together with a mixing device. The mixing device provides different water temperatures based on the outdoor temperature throughout 100% of the heating season, and it is not limited by the boiler manufacturer’s minimum recommended operating temperature. This function provides more comfort by reducing indoor temperature swings and increases system efficiency by reducing system distribution losses.

A modulating output provides a signal which is directly proportional to the actuator position required by the control. Common modulating output signals are a 4-20 mA, 0-135 Ω, or 2-10 V (dc). These signals can also be used to modulate the speed of an injection pump through a motor speed controller.

An on/off device, such as a boiler, must be operated with a differential in order to prevent short cycling. When the supply water temperature drops below the bottom rail of the differential, the device is turned on. The device is then kept on until the temperature reaches the upper rail of the differential. If the differential is set too wide, there can be large temperature swings, and if the differential is set too small the device short cycles and operates inefficiently.

An on/off device, such as a boiler, must be operated with a differential in order to prevent short cycling. When the supply water temperature drops below the bottom rail of the differential, the device is turned on. The device is then kept on until the temperature reaches the upper rail of the differential. If the differential is set too wide, there can be large temperature swings, and if the differential is set too small the device short cycles and operates inefficiently.

When a setback schedule is in effect, the building experiences delays in dropping down its temperature at the beginning of the setback period, and increasing its temperature at the end of the setback period. The optimum start/stop function learns the response of the system in order to calculate a start time for the heating system so that the building is warmed up when the occupied period begins. The optimum start /stop function increase the efficiency of the system and provides more comfort.

In order to properly control a hot water heating system, the heat supplied to a building must equal the heat loss from the building. The heat loss is dependent on the outdoor temperature. It is therefore necessary to reset the supply water temperature based on the outdoor temperature. The ratio at which the water temperature increases as the outdoor temperature decreases is the heating curve. Outdoor temperature reset improves comfort by limiting indoor temperature swings, and provides higher energy savings by minimizing distribution and boiler stack losses.

To provide proper boiler staging and accurate boiler supply temperatures, PID (Proportional, Integral, Derivative) control logic should be used. With PID control logic, the number of boilers fired depends on how far the boiler temperature is below the setpoint, how long the error has persisted, and how fast it is changing. This function provides greater boiler plant efficiency and also prevents water temperature droop that is commonly seen on proportional staged systems.

To prevent excessive room temperature swings and offset, PID (Proportional, Integral, Derivative) control logic should be used to control the zone temperature. With PID control logic, the control operates the zones based on how far the indoor temperature is below the desired temperature, how long it has been there, and how fast it is changing. This function provides more comfort by maintaining an accurate indoor temperature.

Thermostat scheduling allows the room temperature to be automatically setback during the heating season, or set up during the cooling season. Up to 4 events per day may be programmed in order to increase the energy savings of the system. For maximum flexibility, a 24 hour, 5-2 (weekdays and weekend), 5-1-1, (weekdays, Saturday and Sunday), or 7 day schedule may be programmed. Programmable schedules can provide energy savings of 10 to 15%.

PWM is an on/off action that differs from an on/off differential by changing the length of the “on” time based on how much the actual temperature differs from the desired. The heating device is operated based on “how much” heat is required. This function prevents overshoots and undershoots in systems with large thermal mass such as pools or slabs.

Radiant base load uses two-Stage operation to speed up the response of a radiant system. The thermostat operates the first stage of heat to operate the radiant system. The second stage operates a faster response heating terminal, such as a fan coil, to fine tune the air temperature. The end-user can now experience the comfort of radiant floor heating while having the benefit of a faster response heating system.

Remote sensing allows the end user to control the indoor temperature of several zones from one central location. Multiple indoor sensors located throughout the building measure the zone temperatures. Each sensor is connected to a Room Temperature Unit (RTU) which controls the desired zone indoor temperature.

A scene is a state that all zones react to. Each zone may be selected to react in a particular way during a scene. This allows for all the zones to be adjusted to a particular temperature during a specific scene. Building owners can easily select a desired scene from one thermostat and automatically adjust the set-points in all other zones according to the selected scene.

Most set-point loads in a heating system operate year round and often at temperatures above the reset operating temperature. When the set-point load requires heat, this overrides the warm weather shut down and reset temperature of the control. This functions allows the heating system to operate only at the temperature required to satisfy the current load. This saves energy over a system that maintains a constant temperature sufficient to satisfy the highest load.

Set-point priority allows the set-point load to recover faster by temporarily suspending the heat supply to the heating system. All of the available heat is provided to the set-point load for a period of time. This function provides more comfort, by ensuring faster set-point pick up times, and increases system efficiency by often allowing the use of a smaller heat source.

In snow melting systems the slab sensor is normally an inch below the slab surface. When the outdoor temperature suddenly drops, the sensor does not register this change immediately and surface freeze up could occur. The heat input to the slab must therefore increase as the outdoor temperature drops in order to provide a constant slab surface temperature.

Snow melting system deal with extreme temperature differences. Slab protection is provided by limiting the rate of heat transfer into the slab. This is done by slowly ramping up the temperature difference (ΔT) across the slab and limiting the maximum temperature difference. This function prevents cracking of the slab due to thermal expansion caused by high heat inputs.

Snow and ice detection is used to automatically start and stop a snow melting system. When there is snow on the sensor, the sensor melts the snow and ice, detects the moisture and allows the control to start the melting process. This prevents accumulation of snow on the slab and provides a faster response. Automatic snow and ice detection is safer, more convenient and consumes less energy than manual systems.

In systems where snow and ice removal is critical, such as hospital ramps, the pick up time for a snow melting slab can be reduced by maintaining the slab at an idling temperature. The idling temperature may be just below the freezing point. When snow melting is required, the slab temperature is increased.

In snow melting systems accurate control of the slab surface temperature is required in order to provide an energy efficient system. When a snow melting slab operates at a higher temperature, the percentage of energy lost through the back and edge of the slab increase. This function saves energy by accurately controlling the slab temperature.

When a sudden change of supply water temperature occurs, the heating system is subjected to thermal stresses. This is evident in expansion and contraction noises. A change in supply water temperature results from a change in outdoor temperature or a change from a setback period to a recovery period. A soft start allows the control to slowly ramp up the supply water temperature to minimize expansion noises and thermal stresses.

In steam systems the boiler is operated in heating cycles which are dependent on the outdoor temperature. Each heating cycle starts when the system is filled with steam. The steam established function delays the start of the heating cycle until steam is established throughout the system. The steam established function provides more accurate response by accounting for the time that the system takes to come up to temperature.

Some systems such as radiant floor heating must be maintained below an allowable maximum temperature in order to protect the tubing or flooring surface. System protection can be achieved by limiting the supply water temperature to the mixing loop. This function provides a high quality system by preventing potential damage from excessive temperatures.

tekmarNet®4 provides the flexibility to install a programmable thermostat to provide a system schedule that other simpler thermostats can share. Up to four system schedules may be selected by the thermostats. This provides greater functionality while keeping the system affordable.

To provide proper two staging heating and an accurate room temperature, PID (Proportional, Integral, Derivative) control logic should be used. With PID control logic, the operation of the second stage depends on how far the room temperature is below the set-point, how long the error has persisted, and how fast it is changing. This function prevents room temperature droop that is commonly seen with conventional two stage thermostats.

Variable Speed Output is used to vary the speed of a permanent capacitor, impedance protected pump motor of less than 1/6 hp. The pump is piped to inject hot water at different rates from a high temperature loop into a low temperature loop. Variable speed injection mixing provides fast and accurate temperature control and is especially suited for boiler return protection where a fast response is critical.

A glycol solution in snow melting systems increases viscosity at colder temperatures. This reduces the system flow rate and heat transfer. In order to compensate for these changes, the control automatically raises the maximum allowed temperature difference (ΔT) across the slab.

When the slab and outdoor temperatures are warm enough, the snow melting system should automatically turn off. The warm weather cutoff (WWCO) function automatically shuts off the system when snow melting is not required. This saves energy by not allowing unnecessary slab warning.

When the outdoor air temperature is warmer than the indoor temperature, no additional heat is required in the building and therefore the heating system can be shut down. Warm weather shut down (WWSD) provides an adjustable temperature at which the heating system can be automatically turned off. This function increases system efficiency by preventing boiler operation when heat is not required.

By increasing the supply water temperature during the recovery period before the end of the setback schedule, faster pick up times can be achieved. This allows for longer setback periods and therefore more energy savings can be obtained. This function works in conjunction with indoor temperature feedback in order to determine the correct amount of water temperature boost.

When setback is required, the water temperature to the system should be decreased to provide less heat into the space. tekmar reset controls shift the heating curve down in order to provide lower water temperatures when an unoccupied signal is given to the control. The amount that the heating curve can be shifted is adjustable.

Since a zone control calculates all the on times of the zones, a zone post purge can be performed. Before the last zone is turned off in a heating cycle, the boiler is turned off but the zone continues to draw heat from the boiler. This post purge decreases boiler standby losses and reduces overall energy consumption.

In typical zoned systems, the thermostats operate on a stand-alone basis. This means that a zone turns on and off as required without any regard for other zones. The net effect is random operation of the zones causing short cycling of the heat source. tekmarNet®4 thermostats communicate to ensure that their cycles are synchronized. Energy is saved by ensuring that all zones that require heat operate at the same cycle, therefore reducing short cycling of the boiler.