BMS monitoring of an Under Floor Heating (UFH) System
The control system which will be discussed in this report is the BMS (Building Management System) monitoring of a UFH (Under Floor Heating) system serving the MHU (Mental Health Unit) at the Forth Valley Acute Hospital Project covering an area 5800m2. The reason for this being an under floor heating system and not a regular heating system using radiators, radiant panels etc. is to keep rooms free of ligature points and objects which could cause bodily harm. The main function of the system is to monitor the hot water flowing to the under floor heating circuit within the mental health unit maintaining a desired pressure and a set-point temperature of water flowing through the system whilst monitoring for any faults in the system.
The system operates by hot water being pumped to each manifold at a desired flow rate and temperature which is monitored and controlled by the BMS. Each manifold can control up to a maximum of 12 loops and each loop serves an individual room. The rooms have an individual thermostat which allows the occupant to adjust the setting to their desired needs. The thermostat is wired back to the manifold which allows the BMS to control the flow through that manifold to achieve the desired set-point.
1.0 Main Components and Functions
In this chapter the main components of which the system compromises and their functions will be discussed.
1.1 Variable Speed Pumps
There two Variable speed pumps of which one is duty and the other standby, these pumps are used to maintain the hot water through the under floor heating circuit at a desired temperature and flow.
1.2 Temperature Sensor
A temperature sensor mounted in the flow pipework leaving the pump set is used by the BMS controller to modulate the two-port control valve to maintain the required flow temperature set-point through the pumps.
1.3 Differential Pressure Switch
A differential pressure switch mounted across the flow and return pipework is used by the BMS controller to vary the speed of the duty inverter driven pump to maintain a constant under floor heating circuit pressure. Due to each manifold solenoid two-port control valve opening/closing to satisfy the space demands.
1.4 Circuit Flow High Temp Alarm
Circuit Flow High Temp Alarm is used to detect the temperature in the secondary flow pipework and relay information back to the BMS.
1.5 Circuit Flow Safety Valve
Circuit Flow Safety Valve located in the flow pipework leaving the pump set is used to close the system down if the temperature goes above a desired set-point.
1.6 Pump Failed Alarm
Pump Failed Alarm is used to detect whether the pumps have started or not and relay this information back to the BMS.
This chapter will see the discussion of how the BMS controls various components in the system and how the operation of control varies to each component.
2.1 Variable Speed Pumps
The control of the two speed variable pumps can be altered through the BMS to different settings using a HAND/OFF/AUTO switch which provides a facility to start/keep any pump running. When the Pump is in the HAND position the system will be a manual closed loop system as the pump will only be able to be switched off manually. If the pump is in the AUTO position the system will be automatic closed loop system as all aspects of the system are being controlled by the BMS.
2.2 Temperature Sensor
The temperature sensor is part of a closed loop system in which the BMS reads temperature at sensors relays information back to panel and makes necessary adjustments in two-port valve to desired set-point.
2.3 Differential Pressure Switch
The temperature sensor is part of a closed loop system in which the BMS reads the differences in pressure between flow and return due to the two-port valve opening/closing and relays information back to panel and adjusts speed of duty inverter driven pump to satisfy space demands.
2.4 Circuit Flow High Temp Alarm
Circuit Flow High Temp Alarm is a manual closed loop system should the auto-reset thermostat located in the secondary flow pipework detect a temperature above 53 oC an alarm is raised in the BMS which will immediately close the control valve. The plant and alarm will remain in this condition until the temperature has dropped below 51 oC and the fault-button has been manually reset.
2.5 Circuit Flow Safety Valve
Circuit Flow Safety Valve located in the flow pipework leaving the pump set is a manual closed loop system controlled by the BMS to immediately close the direct acting safety valve in the system should the temperature be detected above 55oC. This will raise an alarm in the BMS. The plant and alarm will remain in this condition until the direct acting safety valve has been manually reset.
2.6 Pump Failed Alarm
Pump Failed Alarm should the differential pressure switch detect a pressure ï¿½10% from set- point an alarm is raised on BMS which will start the standby pump and change it to the duty pump. In the case of both pumps failing the circuit is shutdown and an alarm is raised in the BMS. The plant and alarm will remain in this condition until the signal has returned within the limits or fault has been resolved and the fault-button has been manually reset. This system is an automatic closed loop system till a certain point in which it changes to a manual closed loop system.
This chapter will discuss the systems overall performance.
The system has been designed to meet the demand of each individual room within the MHU by the BMS monitoring the room thermostats desired temperature and regulating the flow of water through each under floor heating loop.
Typical system performance for a change in ï¿½1 oC it could take anything from fifteen mins to two hours depending on the ambient temperature for this change to take place.
The system uses lower running temperatures than a normal heating system using radiators and a greater controlling system which is more energy efficient and reduces costs.
This Chapter will discuss how the system could be modified/improved.
The BMS could be set so it monitors outdoor temperature and if the outdoor temperature rose above the required set-point the system automatically adjusted to suit.
Temperature sensors could be strategically placed throughout building to monitor the temperature difference in various areas to allow the BMS to control the desired to flow rate to each area and maintain the desired temperature set-point .