VTS Electric Heaters - Slices

Possible Installation Standards

For VVS and VVSc AHUs, the electric heater made of plasters can be used in two different ways. VVSs heaters are only available in a non-insulated duct variant.

1.1 Electric Heater in a Non-Insulated Duct

Non-insulated duct - all plasters installed in a short duct with a junction box on the side.

When insulating the ventilation ducts, which include an electric heater in this version, ensure that the connection point (especially its ventilation openings) is outside the insulating layer.

Figure 1 - Electric heater in an uninsulated duct

1.2 Electric Heater in the AHU Casing

Full installation in original housing - the heater and its power connection box will be installed inside the "empty section" of the relevant air handling unit. For such an installation, the slices will not be mounted in the duct (blocks mounted directly to the inner surface of the empty AHU section).

Figure 2 - Electric heater in the AHU casing

Scope of Application

The maximum power of electric heaters available for given sizes and types of AHUs is shown below. A full list of the available powers is provided in Chapter 3 - Technical Details.

2.1 Modular AHU - VVS

2.2 Compact Standing AHU - VVSc

2.3 Compact Suspended AHU - VVSS

2.4 NVS AHU

Technical Details

The current version of electric heaters is delivered in two power variants: low power, adjusted to AHUs with relatively low heating demand, and high power, for AHU cases with higher thermal requirements. These types differ mainly in the types of electrical connections of the individual heaters in the assembly (star connection for low power or delta connection for high power).

Appropriate connection between the heaters is made at the heater production stage - the installer only needs to connect the power and control cables - it is not allowed to modify the heater system connections in relation to the factory configuration.

Control

The graphs below show how the voltage supplying the modulated slice changes depending on the required heat demand:

Figure 3 - Modulating the supply voltage depending on the demand for heating power

Each time the modulated slice reaches full power, the demand is transferred to the next slice, which starts working at full capacity. Any additional heating power will be realized by smoothly increasing the adjustable heating power of the modulated slice.

Available Heaters Power Variants for the AHUs - Low Power

Available Heaters Power Variants for the AHUs - High Power

Electrical System Details

Electrical Connection and Protection

The power connection should be made via a separate switchgear, which is not supplied with the VTS delivery. The wiring for powering the electric heater must be led through the panel on the back of the unit. If the cabling is led through the inspection panel from the front side, it should be arranged in such a way as to enable the opening of the section for maintenance and service works.

The connection of the heater should be made in such a way that the heater cannot be turned on when the fans are not working - this is done by factory-installed, serial connected safety devices in the form of a thermostat and a pressure switch, preventing the heater from being turned on if the temperature and air flow conditions are not met.

In case of fan stoppage, it is absolutely necessary to turn off the heater power supply.

The type of cables used for each function of the heaters is presented in the table below (the cable cross-section and its protection should be selected on the basis of the information provided in the tables in Chapter 3 - Technical details).

Heater Wiring

Heater wiring can be divided into two parts:

1. Group of cables with connection independent of the type of heater
2. Group of cables, the connection of which changes with the type of heater and the components used in the AHU

*The connection must be made to the contact No. 24 of the pump relay (K1) located in the AHU automation switchboard.

Views of Exemplary Power Boxes

Figure 4 - Power box – type 1x18kW

Figure 5 - Power box – type 6x18kW

The presented views of power boxes are intended to illustrate the arrangement of components inside their housing. Please note that they are only illustrative - when making electrical connections, always follow the wiring diagrams provided in Chapter 5 - Wiring Diagrams.

Thermostat

The functionality of the thermostat is based on the properties of the bimetallic element - it opens the contacts of the heater control circuit at an air temperature near the thermostat of 65°C. After an emergency switch-off, the heater switches on automatically when the air temperature drops by 20°C. After intentional or emergency (caused by overheating) power off, the supply fan must run for a certain time (0.5-5 min) so that the heaters reach the normal temperature.

The thermostat is an integrated, factory-installed component of each heater slice - it does not require additional assembly or electrical connection by the installer.

Figure 6 - Thermostat

Pressure Switch

The pressure switch is another element, next to the thermostat, protecting against the heater's operation in forbidden conditions. It prevents the heater from being switched on when the pressure generated by the AHU's fan sets is insufficient to ensure safe operation of the heating elements.

Similarly to the thermostat, the pressure switch is a factory-installed and electrically connected component - connection of the pressure hoses of the pressure switch should be made in accordance with the following recommendations:

• One of the tubes should be brought out to atmospheric pressure - in the case of installation of the power box on the duct (outside), the pipe does not need to be connected - there is atmospheric pressure present in the power box.
• The second tube should be connected to the overpressure or underpressure in the AHU or in the duct (before or after the air supply fan).
• In the duct version of the heater, it is allowed to move the pressure switch outside the power box to avoid the need to run long measuring pipes - recommended position of the pressure switch - horizontal, with a vertical position the reading is 11Pa higher compared to the actual one.

The pressure switch switching threshold is 20 Pa. After connecting to the AHU, check if the pressure switch is working properly for the lowest AHU airflow available. In the absence of the detected pressure difference, the place of connection of the second pressure hose to the installation should be changed.

In the opposite case - when for a given pressure switch setting, the pressure difference is detected even when the AHU is turned off (heater operation is allowed despite the lack of fans operation), the setpoint should be gradually increased until the correct operation is obtained - its sign is that the electric heater does not work despite the signals from the control device appearing if the pressure switch does not detect the pressure difference between the measurement channels - the permission should take place only after the fans are started.

After the pressure switch is fully connected, perform the heater shutdown test. To do so, it is necessary to force the electric heater to be manually controlled (e.g. by providing heater control signals from the controller) and at the same time to stop the fans. The pressure switch should prevent the operation of the electric heater (it will be visible e.g. by disconnecting the contactors in the switchgear).

Figure 7 - Pressure switch

Wiring Diagrams

In this chapter, wiring diagrams for each heaters power will be presented, sorted depending on the type and size of the AHU. Pay attention to the following markings:

• Dashed line: CONNECTIONS MADE BY THE USER
• Solid line: CONNECTIONS MADE BY THE MANUFACTURER

For some high power configurations it is required to use two 3x400V power cables, according to a given diagram - this is dictated by the smaller cross-sections of the conductors and the reduction of the required bending radii thanks to this procedure.

For heaters with the capacity of 90kW and 108kW, factory-equipped with two sets of three B32 switches, connect the power cables to the terminals of the central switches of each set!

Green percentages on the diagrams inform about the division of the heater power into the various stages of the heater activation. For example:

0-10V DC = 25%
ST2 = 25%
ST3 = 50%

This notation means that the smoothly regulated part of a given heater constitutes 25% of its power (0-10V DC). The second step - switched on/off (ST2) is also 25%, while the third step - switched on/off (ST3) is 50% of the total power of the heater.

These parameters should be reflected in the appropriate uPC3 driver settings. The settings are made on the HMI Advanced screens:

• -A05 for pre-heater
• -A09 for main heater
• -A06 for re-heater

If in a given system one or both stages switched on/off are not present (no ST2 / ST3 markings in the diagram), the value of 0% should be selected in the controller settings in the appropriate position.

Wiring Diagram for Low Power - 2.5kW - VVS005s

Wiring Diagram for Low Power - 3kW - VVS010s

Wiring Diagram for Low Power - 6kW - VVS015s – VVS030s, VVS021 – VVS030

Wiring Diagram for Low Power - 6kW - VVS040

Wiring Diagram for Low Power - 9kW - VVS055 - VVS075

Wiring Diagram for Low Power - 12kW - VVS100 - VVS650

Wiring Diagram for High Power - 10kW - VVS005s

Wiring Diagram for High Power - 12kW - VVS010s

Wiring Diagram for High Power - 18kW - VVS015s – VVS030s, VVS021 – VVS030, NVS23

Wiring Diagram for High Power - 24kW - VVS040

Wiring Diagram for High Power - 30kW - VVS055 - VVS075

Wiring Diagram for High Power - 36kW - VVS015s – VVS030s, VVS021 – VVS030, NVS39

Wiring Diagram for High Power - 36kW - VVS100 - VVS650

Wiring Diagram for High Power - 48kW - VVS040

Wiring Diagram for High Power - 54kW – VVS030, NVS65

Wiring Diagram for High Power - 60kW - VVS055 – VVS075

Wiring Diagram for High Power - 72kW - VVS040, NVS80

Wiring Diagram for High Power - 72kW - VVS100 - VVS650

Wiring Diagram for High Power - 90kW - VVS055 - VVS075

Wiring Diagram for High Power - 108kW – VVS100 – VVS650

Maintenance Procedure

During the AHU operation (and also before its first start-up), when the heater is not working, dust may settle on the heating elements. When the heater is turned on again, heavy soiling may cause the smell of burning dust or even a fire hazard.

Regularly (annually), especially before the first start-up and before the beginning of the heating period, the condition of electrical connections, the condition of heating elements and the level of their soiling should be checked. Remove any contamination with a vacuum cleaner with a soft suction nozzle or compressed air.

The overheating protection and the pressure protection should also be checked regularly. The air velocity in the AHU during the heater operation should not be less than 1.5 m/s.