Main planning principles of the Hydrokapillare system
Capillary mats are installed directly under the surface of one or several room enclosing
surfaces – either the ceiling, the walls or the floor. Therefore, it is important to assess the thermal conductivity (W/(mK)) of the finishing materials to ensure the required heating and/or cooling capacity in the room.
For example, the thermal conductivity coefficient of KNAUF standard plasterboard White GKB 12.5 mm is 0.21 W/(m.K), while that of KNAUF plasterboard Thermoboard is 0.3 W/(m.K) and of Thermoboard Plus - 0.52 W/(m.K).
The heating and cooling capacity of capillary mats is not a constant value - it depends on the temperature difference between the average water temperature in the Hydrokapillare system and the required room temperature, as well as heat/cold energy transfer in the room is affected by the thermal conductivity of the selected finishing material.
When planning the capillary mat system in the ceiling or walls, special attention must be paid to in determining the cooling capacity, as the above-mentioned temperature difference is limited by the occurrence of a dew point, which is controlled by special sensors.
Due to the large capillary mat exchange surfaces, which can exceed 100% of the heated/cooled surface (if we include the active diameter of all capillary tubes), a significant amount of energy can be transferred without draught and noise even with small temperature differences between the active room surface and air temperature in the room.
Surface heat exchange using Hydrokapillare mats is much more efficient compared to conventional pipe systems due to the small gap (10-30 mm) between the capillary tubes and the large surface area of the mat. This ensures optimal energy transfer to the room. Therefore, only a small difference between the water temperature in the system and the room temperature is required.
It should be taken into account while planning that in the case of heating and/or cooling generated by the capillary mat system, a person feels 2-3 degrees higher (or at cooling - lower) temperature than the air temperature in the room.
For cooling purposes, it is recommended to install Hydrokapillare capillary mats either in the ceiling (under various finishing materials) or in a loosely stretched manner, incl. under a decorative grid. "Gentle" floor cooling is also possible by installing capillary mats in the floor, but a ceiling cooling system is more efficient.
The ceiling surface temperature will be approx. 19°C only at a difference of 2 to 3 K between supply (15°C to 17°C) and reverse (17°C to 19°C). Each control area is equipped with one or more dew point sensors to safely monitor and prevent the risk of condensation. The dew point must be carefully monitored for all surface cooling systems. While the sensor detects condensate, the flow through the mats is stopped either by closing the control valve or by gradually increasing the supply temperature.
This is rare in practice, as radiant cooling ceilings are often combined with support ventilation to cope with latent cooling loads. Ventilation is also required to provide all users with fresh air. The relative humidity here is controlled by ventilation and maintained in a user-friendly and non-critical dew-point range - approx. 50-55% relative humidity. Removal of a reasonable cooling load is done using a radiant cooling ceiling. For this reason, the air exchange rate can be reduced to the minimum hygienically required (approximately 0.3 to 2 times per hour, depending on the type of building), as well as reducing the size and energy costs of the ventilation equipment.
Primary and secondary circuit
Like all weldable plastics, polypropylene is also open to oxygen diffusion. This means that oxygen penetrates through the wall of the pipe into the water until the saturation limit is reached. Unless measures to protect the entire system against oxygen-induced and microbacterial corrosion - which are also recommended when using conventional systems - are planned, two separate water circuits are installed in the Hydrokapillare system and separated from each other by means of stainless steel heat exchangers.
This results in two completely separate circuits which are known as the primary circuit (cold/heat source to heat exchanger) and secondary circuit (from the heat exchanger to the mats). The heat exchanger is part of a compact transfer station in the secondary circuit which consists of the circulation pump and the expansion vessel, among other things. All components having contact with water in the secondary circuit must be made of corrosion-resistant materials such as plastic, stainless steel, bronze or brass.
Nowadays there are models of heat pumps and gas boilers available which do not contain any elements that can cause corrosion in the system. In such cases the heat exchanger isn’t necessary. It’s recommended to check the specifications of a particular model of heat pump or gas boiler (including the circulation pump housing) before the planning stage of the system is completed.
Water is filled in the secondary circuit only once during the system installation process, and water circulates in a closed circuit.
System control concept
As a result of the low water content and the spreading of 2 K or 3 K, the zone control is effected as a two-point control (on/off). As a rule, a constant control of the water flow is not considered practical as the two-point control is effective enough. Depending on the control signal of the room temperature controller, the electro-thermal actuator on the relevant zone valve either opens or closes. Zone temperature control occurs separately for each zone where the set point can have both centralized and decentralized adjustment. A switch over between heating or cooling operation can also be carried out centrally.
In addition, in case of cooling, each zone is equipped with a dew point sensor. This has only the function of a safety device which either shuts off the zone where there is a danger to reach a dew point – even if the room temperature is above the set point – or it gradually raises the supply temperature according to the relative humidity of the room and/or the enthalpy of the ambient air condition.
Manifolds for the Hydrokapillare system
Supply and return lines of individual zones are connected to manifolds. There are different models available with 2 to 16 outlets.
Important! Connection of max 18 m2 of capillary mats can be planned per each hydraulic circuit.
The connection of the capillary mats to the manifold is made with welded PPR pipes PN10 and fittings of the required diameter.
You can find manifolds suitable for the Hydrokapillare system in our Product catalog ›
Valves for water flow control and hydraulic balancing
In principle, all commercially-available valves and armatures can be used within the capillary mat system, provided they fulfill the requirement for corrosion resistance.
Each zone of the system requires the installation of armatures for shutoff, hydraulic balancing and a control valve. For shutoff purposes, corrosion-resistant ball valves made either of stainless steel, bronze, brass or plastic can be used. The hydraulic balancing is effected by means of line-type regulating armatures (Oventrop, Heimeier, Taco, TA and similar types) which allocate their setpoint mass flow to the individual zones. From thermal aspects, the zones are normally controlled by means of a 2-point-valve.
This simple open/shut control mode is fully adequate due to the low level water content and the low inertia of the system, particularly in view of the fact that a constant control with a 2 K spreading would not be practical and would involve high expenditure. For smaller dimensions and system pressures, thermo-electric actuators 24V and/or 230V are normally used. For higher system pressures, actuators with E-motors are applied. The transitions of the valves/armatures, normally provided with threads, to PP is established by means of transition form parts metal/plastic which are welded into the plastic piping.
A standard hydraulic module consists of the following elements:
- adjustable, corrosion-resistant circulation pump (WILO, GRUNDFOS Magna, etc.);
- stainless steel heat exchanger (if necessary);
- two manometers 0 - 4,0 bar;
- two thermometers 0 - 40°C;
- brass membrane safety valve;
- two ball valves with hose connection;
- shutoff ball valves, with pipe nominal width of main supply and return lines;
- membrane expansion vessel, drinking water design type.
The configuration of the hydraulic module depends on the technical parameters of the selected heat/cold energy source.