Fan coil control in Doha Metro
The Doha Metro
Since 2016, Domat Control System takes part at the supply of components for building management system of the Doha Metropolitan, Qatar. As this was one of major
international projects for Domat, let’s have a look at some of its features.
The entire metropolitan is planned as four lines with 85 stations in total, three lines being in construction. The first line is about to be completed in 2019. Their total length is more than 200 km. Stations and their environment are a significant part of the project, containing shopping and office facilities.
Domat supplied to Lysys, the local partner, room cooling controllers for shopping and office areas. More than 1000 fan-coil controller and the same amount of room units have been shipped so far.
The FC025 hardware origins from the FC020 fan coil controller. The FC020 controls a three-stage fan and, unlike the smaller FC010, contains also analogue inputs and outputs and more binary inputs., The complete I/O mix looks as follows:
|AI||4||2× resistive (0…5000 Ohm) or 0…10 V, 2× resistive (0…5000 Ohm)|
|DO||7||3 relays 230 V / 5 A, 4 triacs 24 V AC / 0.4 A|
The controller also features two RS485 interfaces with Modbus RTU: one for the UC010 room unit and optional slave controllers, one for integration to a BMS (Building Management System). The communicative room unit UC010 may be replaced or enhanced by a passive temperature sensor and optionally a potentiometer to set a room setpoint correction. This is used at sites where users should not be allowed to intervene with the system, such as in schools, public buildings, or hospitals, or the customer requires a special room unit of the same design as the other components (sockets, switches) in the room.
Another controller type, FC026, was customized also regarding the I/O mix:
|AI||4||2× 0…10 V, 2× resistive (0…5000 Ohm)|
|DO||4||triacs 24 V AC / 0.4 A|
The HVAC system contains EC fans controlled by 0…10 V DC rather than three-stage fans. EC (Electronically Controlled) fans have become an excellent alternative to traditional three-stage fans lately – they are easy to wire, can be controlled continually from 0 to 100 % and they do not contain capacitors for speed control, which have often been a cause of problems. There is an extra analogue output in the controller rather than digital outputs for the fan. Analogue outputs are used for EC fan control, cooling valve, and indication of room temperature to the building management system.
The firmware was modified so that the controller provides hardware inputs and outputs for data exchange with the building management system. The following signals are used:
AI (BMS to FC): room temperature setpoint
AO (FC to BMS): measured room temperature
DI (BMS to FC): fancoil operation enable
DO (FC to BMS): fancoil operation indication
DO (FC to BMS): alarm indication
The fancoils are used for cooling only. Not very common datapoints for a fancoil plant are inputs to monitor valve position, filter differential pressure switch, and fire emergency shutdown input. Both Domat and Lysys expected that there would be more design changes in the course of time, so the functionality was as configurable as possible. Some of the options were analogue input ranges (0…10 V or 2…10 V), measured value selection (external sensor or room unit), sense of the binary inputs (NO / NC), and function of the binary inputs (presence or filter alarm).
The whole project took about two years, which is relatively a long time. Most of the time was spent on technical clarification. Usually, the complete development does not exceed 6 to 9 months, even when both hardware and firmware are customized. In this case, the first talks began on autumn 2016, the complete function description was finished in February 2017 after several conference calls, and the approval process was finished no sooner than in May 2017. The staple document for approval was the data sheet with detailed functional description, terminal layout etc., stamped and approved by customer.
In June 2017, the first controllers were manufactured together with firmware for the first tests. The tests took about a week, and minor bugs and unclear issues were fixed. Then the first batch was completed and deep final tests were executed. The first shipment followed by end of August; the whole order was split into several parts according to the manufacturing capacity and orders for the construction phases. In November 2017 to January 2018 the controllers were mounted into distribution boxes and the engineers were trained in commissioning.
The commissioning itself took place in March to June 2018. Several requests for changes originated in this phase, some default parameters were changed in the firmware. Some of the controllers were damaged by wrong installation or bringing 230 V AC to low-voltage terminals. It was about 16 controllers in total, which are less than 2 pct. of the whole shipment.
There were no major problems at hand-over, apart from two events: several room units were damaged by smoke and soot which entered the installation boxes through the plastic installation pipes from technical rooms where there was apparently a fire. At the first sight, it looked like the room unit burned, but it was explained later: the less damaged units were not thermally damaged, just covered with soot. The track lead to the installation piping. In the second case, the project manager claimed the room sensors faulty, having measured about 2 K higher room temperature with a test probe than showed by the room unit. This was fixed by repositioning of the sensor and introducing minor corrections on measured values.
International projects in this region have got a huge potential. To complete them successfully, suppliers have to be aware of some differences against local project management:
The supply chain and project management chain is complex. Metro Doha is not a simple project, and its „food chain“ was complex, accordingly. The whole project was divided to several sites, every site having different supplier general who contracted its sub-suppliers. If components of a single brand had to be supplied for the whole project, which was the case of fan-coil controllers, the brand supplier worked for several customers with minimum mutual coordination. Moreover, every management level (investor, supplier general, the construction firm, building technologies supplier etc.) employed a separate consultancy firm who was responsible for the technical part of the project. These consultants showed to be the „most complicated“ partners, as they required explanation and justification of – from our point of view – proven and standard solutions. For example, integration of the controllers to the BMS follows over analogue and binary signals rather than over a communication bus. Data integration would be much easier and could provide much more data for both operation and commissioning.
The communication followed with no problems, our customer has been working with us since several years, and there were relations on a personal basis. It was necessary to do with longer reaction time before the information penetrated all the layers mentioned above, however, the response had to be quick as the partner was usually in a time press. The development department had to think in advance and get ready several options which the customer had to choose from. It is a safer way than let the customer think up a solution which can be executed with problems or not at all.
In Qatar, Sunday is a working day (and Friday is free), so it was a bit incomfortable that urgent mails and phone calls arrived at the Sunday lunch time when there were inspection times and meetings at the site.
All documentation must be compiled very carefully and no prior knowledge shall be expected from the customer. The data sheets and manuals are used by workers who are operating in a very different cultural environment, and may work with the supplied technologies for the first time. No information provided is redundant or obsolete. The documentation may serve later as a justification of a well designed, but wrongly installed or operated product. The data sheet, for example, contained also a block diagram of the controller functionality.
The technical support was easier thanks to the fact that the controllers are set up over a serial line and a simple configuration program. It allows to export the complete setting of a controller into a file which can be sent oby e-mail to the support engineer who is able to duplicate the exact setting of a controller at his desk. After parameter correction or setup change, the file is sent back and simply uploaded to the controller by the customer. This was how some problems due to wrong binary inputs configuration were discovered and explained.
The whole project was slightly more demanding than projects of similar magnitude in Europe, but it was successful in the end and we believe that also the other Doha Metro lines climate will be controlled by the Domat room controllers.