Proper functionality of air handling unit depends on its quality, as well as on the quality of supporting equipment and installations and the method of their connection. One of the key external installations is the process heat installation which supplies the water heater. A heating power regulation system, consisting of a tee-valve, a pump and accessories, has to be installed at the site of the water heater connection. It is a seemingly easy task. However, errors often are committed in practice, which makes it impossible to regulate air temperature in a proper way.
The contractors often confuse the manner of connection of a mixing and separating 3-way valve. It may happen that valve and pump parameters or the parameters of other components, selected individually by the contractor, do not match with one another. Another difficult issue is a correct and aesthetic design of the heat insulation for many combined elements (the valve, the pump, the filter, bolt fasteners) in a manner which enables their servicing.
Responding positively to the need of rapid, economical and fault-free connection of these installations, VTS have completed their sales offer of air handling units with pump centres to ensure optimal matching of complete system parameters, responsible for air heating in air handling units.
VTS pump centre combined with VENTUS 2016 air handling unit
VTS pump centres – are hydraulic systems, housed in a separate casing, intended to control the heat power of water heaters of the air, used in air handling units. They can be used in case of heating medium temperatures not higher than 120°C, at acceptable pressure of 10 bar. The maximum available pressure (the elevation height of the complete set) depending on the type ranges between 7m and 10.5m of water column. The selection of the appropriate value is possible, using ClimaCAD OnLine (CCOL) software or on the basis of ready characteristics, contained in the operation and maintenance documentation.
Operating description
Pump centres are responsible for qualitative regulation of heating power of water heaters that consist in the change of temperature of the working medium supplied to the heaters while maintaining relatively constant medium efficiency.
The temperature of the working medium upon the supply to the heater can be obtained by the mixing of the colder medium coming from the heater with the hot medium from the supply installation in the control valve. The constant flow of the medium before the heater is enforced by means of the circulation pump, and the quantity of the hot medium obtained from the source is regulated by changing the degree of control of the three-way valve.
Operating diagram
Advantages resulting from the use of ready-made pump centres
The application of ready-made power control systems of water heaters is, first and foremost, a convenient and easy solution for contractor companies, eliminating connection errors and guaranteeing the optimum adjustment of technical parameters of specific components of these systems. The method of qualitative regulation used offers a possibility to apply double, most effective anti-freeze protection of the heater, based on return heating medium temperature measurements, active also when the air handling unit is off, and on air temperature control with an anti-freeze thermostat. An additional fitting of connection spigots with thermomanometers offers the possibility to monitor in real time medium temperatures and pressures, both on supply and on return from the heater.
A selection of pump centre is made by means of the CCOL software, in one cycle with air handling unit selection, which is an unquestionable attribute of this solution, since it guarantees, apart from selection ease and convenience, also an optimal adjustment of the complete air heating system in VENTUS air handling systems. It also guarantees an optimal support of VTS control system.
Structure
The main pump centre components include: circulation water pump, three-way control valve with cylinder, mesh filter, two thermomanometers, as well as two shut-off valves. The whole assembly is housed in a casing of EPP foam which, with its very good insulation parameters, effectively protects against heat loss, while also ensuring protection against mechanical damage and weather conditions.
VTS pump centre
Why is heater power control qualitative and not quantitative?
The construction of buildings and building technology allows for application of both quantitative and qualitative water heater power controls, however, in case of quantitative control, heating power reduction is achieved by performance reduction of the medium flowing through the heater, which can lead to its freezing in wintertime, despite of efficient anti-freeze thermostat operation at heater outlet. Multi-row exchangers, commonly used in ventilation systems, are particularly at risk. This is due to the fact that high heat exchange performance is achieved by medium-air counterflow configuration, in result of which pre-cooled medium is pumped into the cold outdoor air zone. Low medium flow rates that can occur in the process of quantitative temperature control also in wintertime expose the medium to deep cooling – up to freezing.
With the view to minimising the risk of heater damage, the systems, offered by VTS, use qualitative heating power control, in case of which a nominal medium stream always flows through the heater, thus being significantly less susceptible to deep cooling and freezing that occurs in case of quantitative control. Moreover, a constant medium flow through the heater, ensured also when the valve control is set to zero, enables constant measurement of actual temperature values at the coolest zone of the return line from the heater. VTS automation by means of appropriate valve control prevents excessive temperature reduction, thus providing the most effective anti-freeze protection of the heater, active when the air handling unit is on and off (the majority of freeze failures of heaters takes place upon switching off air handling units when the classic anti-freeze protection, offered by the thermostat installed behind the heater, is not effective).
The products will appear in the VTS offer at the beginning of May. Nine pump centre types will be available, differing in medium flow rates and hydraulic resistance levels (taking into account the authority of the three-way valve).
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