ISO 11855-6 pdf download – Building environment design — Design, dimensioning, installation andcontrol of embedded radiant heating and cooling systems — Part 6: Control

ISO 11855-6 pdf download – Building environment design — Design, dimensioning, installation andcontrol of embedded radiant heating and cooling systems — Part 6: Control.
The control system classification Is based on performance level:
1) Manual: The energy supply to the conditioned space is only controlled by a manually
operated device
2) Autoniatic A suitable system or device automatically controls energy to the conditioned spaces
3) Timing: Function of energy supplied to a conditioned space is shut oIf or reduced during scheduled periods, e.g. night setback (not necessarily applicable for cooling)
4) Advanced timing: Function of energy supply to the conditioned space is shut-oft or reduced during scheduled periods, eg. daytiiiie with more expensive electricity tariff. Re-starting of the energy supply is optimized based on various considerations, including reduction of energy use (not
applicable in commercial buildings)
4.2 Central control
The central control shall control the water temperature through the embedded system. In residential systems the control Is normally done according to the outside climate (based on the heating/cooling curve, which is influenced by building mass, heat loss, and differences in heat required by the individual rooms) control the supply water temperature to the system.
To reduce losses in the distribution system the central control must control according to outside temperature, i.e. higher water temperature for lower outside temperatures, for heating only.
Instead ofcontrnllingthe supply watertemperature it Is recommended to control the water temperature (supply and return water temperature) according to outside and/or indoor temperatures. This is more directly related to the energy Ilux into the space. If during the heating period for example the Internal load in the space increases, the heat output of the floorsystem will decrease and the return temperature will increase.
lithe embedded system is operated intermittently (e.g. night and/or weekend set-hack) the central control is also important for providing high enough water temperatures (Boost effect) during the preconditioning period In the morning. The energy savings by night set-back in residential buildings are. however, relatively law due to the high thermal insulation standard in new houses.
For commercial systems the control Is normally done according to the heat loss or gain, and differences in heat or cooling required by the individual rooms which control the supply water temperature to the system.
For cooling it is also recommended to control the supply water temperature based on the zone with the highest dew point temperature. In many buildings with cooling, the internal load is of significant Importance and it is recommended to let the room temperature and humidity of representative space influence the control of the water temperature.
Radiant surface cooling systems shall include controls to avoid condensation on internal cooled surfaces or condensation in critical parts of the building. This can be done by a central control of the supply water temperature and a limit on the minimum water temperature based on a measured dew point in the conditioned space.
In the case of a radiant surface heating system, the valve (and then the water flow) on the manifold is controlled by a room sensor (wired or wireless). The wiring is often installed together with the main power wiring. Room sensors are therefore often Installed near a switch for the main power (door), and not in a representative position of the occupied zone. In order to eliminate this problem, individual room temperature control systems, using a link based on radiofrequency transmission between the room sensors and the control valves (Figure 1), can improve the quality of the control.
In terms of comfort, it is preferable to control the room temperature as .i function of the operative temperature in thearea occupied by the person. Hesides the position, It is important to consider the shape, size and colour (important for short wave radiation, sun lights) ofthe sensor in order to express convective and radiant heat exchange between sensor and space similarly as for the person (refer to EN 7726).
4.5 Influence of thermal mass of embedded systems
The heat capacity of surfaces with embedded pipes (e.g. as the floor screed), play a significant role for the thermodynamic properties of the heating system and hence for the control strategy. The temperature level of heat carrier, the time response and the thermal capacity of systems will depend on the thickness of the surface layer where the pipes are embedded. The highest capacity involve systems E. F with slow response to load changes on water side in concrete core followed by Tpes A, C, D, B and the lowest capacity gain systems typed as G. In most cases the time constant of the building is several times higher than embedded systems.