DEW POINT MANAGEMENT
- Marco Serpelloni
Introduction
The REG System is specifically designed for radiant cooling system and provides some algorithms to prevent condensation from forming on the radiant surface during summer operation.
The system calculates the Dew Point Temperature (Dew Point) for each zone equipped with a temperature+humidity sensor, that is the critical temperature below which condensation forms under the zone’s current conditions.
The Dew Point Temperature, corrected by an offset that can be set differently from zone to zone (Dew Point Control parameter, indicated as Ctrl DP in the Configuration Zone/1 sub page), is compared with the Outlet temperature of the circuit serving the zone; if the water temperature is equal or below the calculated limit, there are the conditions for condensation formation.
If the circuit serving the zone is equipped with a mixed valve controlled by the REG System, the Outlet temperature of the circuit is increased if the water temperature is too close to the Dew Point Temperature, otherwise the zone will be blocked.
Note
For zones used as “Integration” to the dehumidifiers in Cooling system, the Dew Point Control (Ctrl DP) value must be set very high (in the order of 20°C), because the associated user does not act directly on the radiant surface, but it is a “Support” to the action of the dehumidifier.
Temperature Control and Zone Locking
The REG System is able to manage, in a smart and flexible way, the condensation in two main ways:
Circuit Water Outlet Temperature Control
Zone Block
Both controls require the installation of a water probe to control the water temperature of the circuits/manifolds, while the water outlet temperature Control required the presence of a mixing valve or the ability to send the set point directly to the cold-water source (via 0/10V, Modbus, or OpenTherm).
If there is no water outlet probe connected when the system needs to compare the result of the dew point calculation, it will use the value indicated in configuration/1 “Theoric Dew Point Limit”:
It is obviously not recommended to use this mode of dew point management.
1. Calculation of Surface Temperature
A condensation condition occurs when the floor surface temperature drops below the Dew Point. The water outlet temperature probe may be colder than the floor surface temperature, which depends on the materials used for the finish (wood, tiles, etc.). the REG System has a parameter, within the Zone section and different for each zone, which allows to considerate this factor.
For a correct operation of the system, it is recommended to correctly set the value of the Ctrl DP:
Radiant Surface Material | Dew Point Control |
|---|---|
Marble | 3,0 °C |
Ceramics | 3,0 °C |
Wood | 4,5 °C |
The values of the Dew Point Control (Ctrl DP) given above are indicative as it can vary depending on the materials used for the system construction. In fact, it cannot be excluded that two surfaces with the same material may have different values; this difference can depend on several factors:
Screed thickness
Materials used for floor construction
Radiant system pipes materials
Note
Within the Zone section (in the red frame), for each zone equipped with humidity and temperature sensor, the Dew Point (°C), indicated by the abbreviation DP in the green frame, is calculated:
for the zones without humidity sensor, the DP is NC, not calculated.
The calculated DP must be compared with the floor surface temperature, which is the sum of the cold-water temperature and of a delta that take into consideration the type of covering. The parameter that allows the delta to be taken into account is the Dew Point Control (K, Kelvin degrees are used to indicate that the parameter is a temperature difference and not a temperature value), indicated by the abbreviation Ctrl DP in the green frame:
Let us, for example, consider the zone 2, for which the calculated dew point is 16,1°C and the Dew Point control is equal to 3 K. The calculated dew point (16,1°C) will not be compared to the value read by the water outlet temperature of the circuit associated with the zone (C1), but with the value read by the probe of C2 + 3 K. Zone 1 will be blocked to prevent condensation if the water outlet temperature of the associated C2 circuit is less then 13,1°C (16,1°C - 3 K). While zone 1 will be blocked if the water outlet temperature of the associated C2 circuit drops below 15,3°C (18,3°C - 3 K). And in the above image this happens since the Output is off.
To the right of Ctrl DP is another column marked 0. This column ensures that the calculation of the temperature to be compared with the calculated DP takes into account not only the water temperature, but also the room temperature. The value in the box can range from 0 to 100 (dimensionless):
If 0 is indicated, it means that the room temperature is not considered in the calculation and that simply the DP is compared with the water outlet temperature + delta K of the Ctrl DP box;
If 100 is indicated, it means that water temperature is not considered in the calculation and that the DP is compared with the room temperature of the zone;
If a value between 1 a 99 is indicated, then a weighted average of the two temperatures is calculated to find the reference temperature to compare with DP. For example: I use 50, this means that the temperature to be compared with DP is = [(room T * 50) + (Outlet T + delta K) * 50]/100
2. Water Outlet Temperature Control
Before blocking the zone, the REG System tries to increase the water temperature by closing the mixing valve or by increasing the set point at the chiller (via 0/10V, OpenTherm, or Modbus).
To do this, the REG System uses the parameter Offset DP/Water Outlet T, highlighted in yellow in the Configuration/1 page; it is an increase given to the water Outlet temperature of all circuits to avoid being too close to the calculated Dew Point. This logic avoids the repeated lockout and unlocking of the zones as it protects against condensation by raising the water outlet temperature, before the zone block intervenes.
Considering, for example, to use 1,5 K as Offset DP/Water outlet T and having a zone which is connected to the circuit 1 which is at risk of condensation if the water outlet temperature < 15,1°C (calculated DP = 18,1 °C and CtrlDP = 3 K with 0 = the room temperature is not considered), it can be seen that the lower outlet limit is 15,1°C + 1,5 = 16,6°C, which also corresponds to the set point (desired temperature) > 15°C which would be the set point of the cold circuit in Comfort mode:
Obviously, the Offset/Outlet applies to all circuits when only one of the connected zones is at risk of condensation. It could be that other zones are not at risk of condensation and the increasing of the water outlet temperature to avoid a single zone from blocking prevents the other zones from being cooled.
If you want to limit the effect of Offset / Outlet on a circuit, you must use the parameter “Dew Point Correction Limit”, which is a temperature value (not a delta):
If left at zero, it is as being switched off. If different from zero, it represents the maximum increase allowed for that circuit. In the example below, 18°C represents the maximum increase, above 18°C the set point in cooling will not be raised:
At this point, the zone block will intervene for the zone at risk of condensation, but the rest of the system can keep cooling the zones not at risk of condensation.
3. Zone Block
When the water outlet temperature control fails, the zone will be locked (Output OFF) by closing its header. Once the zone is locked, it will restart by considering the Dew Point Hysteresis set in the Configuration / 1 (in the green frame):
So, in the example of zone 6 in the second image, if it were block, it would be restarted with calculated DP = 14°C if the hysteresis was 1 K as shown in the image.
Furthermore, when the zone is locked, the associated dehumidifier, if present, will be switch ON, even if the detected humidity is lower than the humidity set point.