Proposal of a cooling circuit for 1 ECAL Super Module

17/01/2002
Arnaud Hormière ST-CV

Back

=> Introduction

=> Former Work

=> New parameters

=> Philosophy

=> Hydraulic Plans

=> Temperature Measurement

=> Process Regulation and Control

=> Installation in zone H4

=> Budget

=> Industrial Contacts

Several steps of the development of the ECAL subdetector have been delayed, essentially due to the difficulties encountered in manufacturing the final electronic cards (VFE). The design of this card has evolved, with consequences on the power dissipation per channel of the detector. This has major consequences on the dimensions of the cooling circuit dedicated to this detector. It implies changes in the cooling station (pumps, heat exchangers...) and all along the routing for the pipes, also in the detector. The "power to cool" by the cooling circuit has to be reviewed, as changes in the electronic card may change the dissipation in the Low Voltage cables, supposed to be cooled by the Power cooling circuit of ECAL (some information on the former values can be found in "Power to cool" review).

Former Work

Some work has been done concerning a cooling circuit for a Super Module, including a partial Cost Estimate. This work is considered as a base for the current proposal.

Power Circuit

Regulating Circuit

Cost Estimate (not finished)

New Parameters

Formerly, the heat dissipation per channel for the electronic card was set to 1.7. It is now supposed to be 2.5 W/ch, but the design value will be 3 W/ch. These values were given during the 21st SPES meeting, 14 November 2001.
We will calculate the new heat dissipation in a Super Module (1700 channels) and the consequences on the flow rate.

Total heat to remove: 5.1 kW. (90% Power circuit and 10% Regulating circuit).

Flow rate:
Once we have the heat to remove by each circuit, we compute the flow rate with the temperature difference allowed between the inlet and the outlet of the detector for each circuit. However, some parts of the circuit inside CMS have already been designed and the diameter of some pipes has been fixed (Crack 53°). As we don't want velocities bigger than 2 m/s, it gives a limit value for the flow rate.
Values to be used for all EB, 36 Super Modules(O.Teller EP/CMA): Power: 10 l/s and Regulation: 50 l/s.

Pumps:
The pumps will be equipped with variable speed drive (see below). To design these pumps, we have to give a range of flow rate and head. We design them such as the can provide twice the nominal flow rate given above. For the head loss, it is computed from the circuit path.

Pipes diameters
Calculated to have a maximum speed of 2 m/s with the maximum flow rate.

Pumps power:
The maximum pump power is calculated as follow: Efficiency*Hydraulic power delivered.
Efficiency=1/0.7 and Hydraulic power=Maximum Flow rate * Maximum head.

Heater:
Designed to increase the temperature with 0.2K for nominal load, witha maximum of 0.3K.

Heat to remove:
The heat to remove comes from the detector and the pump (and also the heater for the regulating circuit). We use the maximum pump power and the add a margin that correspond to a change in temperature of 1K for the power and 0.1K for the regulating (equivalent to 20% margin).
As there is two heat exchangers and two loops in the regulating, we have to increase the heat to remove for the heat exchanger to the primary. This can be estimated to a 10% duty margin on the heat exchanger.

Flow in the primary:
It is possible to estimate the flow rate in the primary for both circuits, assuming a temperature difference of 6°C. It will give the minimum flow rate. The maximum can be estimated to be twice this minimum flow rate, it is mainly for pipe dimension's safety margin.
The pressure drop between inlet and outlet line is estimated to 3 bars in the caverns. The value of this pressure drop for the prototype will depends on the location of the cooling station itself.

Remark:
It is important to notice that some work has to be done concerning the power circuit. It is presently under development and some constraints may increase the flow rate. The main reason  is to allow a minimum Reynolds number in the cooling tubes for an efficient heat transfer.

Philosophy

• Choice of technologies
  The cooling station for a super module will be a test bench to set the hydraulic parameters and the regulation needs and possibilities for the final ECAL cooling circuit. This implies that the results obtained with this prototype are relevant for the final circuit. For this reason, the hydraulic parts (pumps, heat exchangers...), the measurement and control technologies are chosen for their range of utility, i.e. they have to be suitable for the prototype and the final circuit. This is done to avoid mistakes done in the Module0, where the use of the Lauda as a chiller for the regulating circuit is of no use for further development.

• Use of Quick Coupling
  Several tests will be performed on the Super Module (SM), and some will require to disconnect it from the cooling station. Some quick coupling connectors with no spill will be used to link this two parts. Care is to be taken if this station is used for the calibration of the SMs, to avoid to buy this type of connector for every SM.

• Instrumentation
  As it is mentioned above, this cooling circuit will be a test bench. Especially for the regulating circuit, the phenomena of heat transfer has to be well understood. For this reason, several parameters have to be monitored. In the Module0, some information is lacking, especially for the chilled water in the primary circuit. It is a problem, as a variation in the primary circuit can affect the conditions in the detector circuit. This instrumentation will be important for the Super Module as we don't know yet the conditions that can be encountered in the primary circuit.
  The list given below is a non exhaustive list of instrumentation recommended. Some of them can be only visual indicators, but most of them have to take part of the supervision process.
  For the primary circuit (Power and regulating): flow, pressure and temperature. These measurements do not have to be very precise.
  Regulating intermediate circuit: Flow and temperature.
  Regulating detector circuit: Temperature in several points, some very precise, pressure drop in the detector, pressure in some points, flow.
  Power circuit: Pressure drop, pressure in some points, flow and temperature.

• Variable speed drive
  The pumps should be equipped with variable speed drives, either already with the pump engine or in the electrical cabinet. It is a very simple way to regulate the flow, more precise than an hydraulic by-pass, and quite cheap for the power involved in this circuit. This will allow a range of possible flow rate, to perform easily hydraulic tests, and find the best solution. A range of flow must be determined as it was done for the pressure loss.
  Pressure gauge should be placed at the inlet and the outlet of the pump to know roughly the head given by the pump.

• Re-use of components
  Care should be taken in the choice of components for their re-use ability. This is especially true for the instrumentation and control components that are expensive. For example, the flow measurement can be done with a differential pressure measurement device rather than a paddle wheel, if the costs are similar. The precise temperature probes have also to be chosen with great care due to their cost.

• Expansion Vessel
  The volume of the circuits can be evaluated to 100 liters for the regulating circuit and 25 liters for the power circuit. The thermal expansion of this volumes is less than 1 liter for a 30 degree variation, which is a lot more than expected. From a security point of view, the choice of the expansion vessel is not critical.
  Two types of vessel exist. the first one is with a fixed charge of gas and the second have a variable charge of gas. the first type is very simple and cheap (~200CHF), the second one is bigger, more complex and expensive (~4000CHF) but allows different functionalities.
  Type1    Type2
  For the intermediate loop of the regulating circuit, a type 1 is sufficient. For the detector circuit, that will be emptied and filled several times, it depends if an operator can fill the circuit and check the pressure in the vessel. If so, a type 1 is the appropriate solution. If it is not possible, type2 should be chosen. It allows an automatic control of the pressure in the circuit, it is also a good indicator for leakage detection.

• Externalization in the Budget
  The cost estimate is done considering that none of the work is done at CERN, apart from the operation.

Hydraulic plans

Power circuit

Regulating circuit

Temperature Measurement

It is difficult to find a level of precision of ± 0.05 K and a good repeatability in the measurement with the classical temperature measurement devices used in industry, i.e. probe and transmitter. Several companies have been consulted, and large ones like ABB Automation and Rosemount, but the solution proposed is not sufficient. The problem doesn't come from the probe itself (even if it must be of good quality and with a low response time) but from the transmitter, that measure the resistance of the Pt100, and convert it to a temperature.

For a Pt100, in a first approximation, we can say that a variation of 0.4 ohms of the resistance is equivalent to a variation of 1K of the temperature. If we want to measure 0.01 K of variation accurately, the transmitter must be able to measure 0.004 ohms, that is, for a measure of ~ 100 ohms, 0.004 % of error on the measurement.

An alternative solution could be to use apparatus used in laboratory, like the acquisition unit from Agilent Technologies (34970A). It is a precise multimeter with a multiplexer, that allow several measurements (Data sheet) . It gives far better results compared to the transmitters and for a better price.
The problem with this device in our application comes from its communication with a PLC. It is possible through the RS232 port (in ASCII), but some development has to be done to ensure the communication.

Process Regulation and Control

The level of performance required is far above the classical needs. To reach such a level, advanced and high performance control has to be used (multi variable, predictive controller...).

Process control diagram

To ensure such regulation, and with the same level of reliability as normal automated process, the best solution is to use a Quantum PLC from Schneider. It is already used at CERN for some applications (ST/CV cooling towers), and is foreseen for the control of LHC cryogenic supply. It is a very powerful automaton for calculation, and it is design for advanced control (with build in predictive loops and libraries).
The following diagram shows the control architecture, including the data acquisition unit for temperatures.

Control architecture

Remark: For this topic, a non negligible help was provided by D.Blanc and M.C. Morodo Testa from ST/CV.

Installation in zone H4 of B.887

Cold source
The activity of calibration in the H4 zone will request some cooling power apart from the cooling of ECAL Electronic cards, for ventilation in the area and for other electronic devices.
Nowadays, this cooling power comes from the chilled water circuit of the CERN facilities. The installations are connected to this circuit through DN50 pipes (Situation map at 10 December 2001). The cooling station can be installed either inside the barrack or outside, depending on the surface needed and available.
A connection to this actual DN50 pipes has to be foreseen for the heat exchangers primary water.

Demineralised water access
The cooling circuit will be open and reconnected when passing from a super module to another, and the new super module will have to be filled with water. This operation will be done at least 36 times, as there is 36 super modules. For this reason, it must be possible to fill easily the circuit. A connection has to be done between the demineralised water network in building 887 and the cooling rack. 

Gas for purging and expansion vessel
The installation of an expansion vessel that can be filled directly with demineralised water and also linked to a gas source is a possible solution. It is also an indicator of leakage, if some gas is needed to maintain the pressure in the vessel under operation.
The cooling circuit will also be purged when passing from a super module to another, to empty the super module that has been tested. This operation can be done with an injection of nitrogen. In this case, a gas circuit has to be installed in the H4 area.

Purging scenarios for SM
Not yet determined

Budget

This budget is for a solution using a Quantum for regulation and control. It includes manpower and material, also some piping in the H4 zone.

The price of the Power circuit is smaller than the price of the regulating circuit. It has less material, so less handwork on it and is not insulated.

The Control and regulation is a major part of the cost. In this case, it is not linked with the size of the process, but with its complexity.

TOTAL: ~200 KCHF

Details: (without control and regulation costs) PDF File

Industrial Contacts

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