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Telescope Cooler (glycol) System Report
Paul T. Worthington

April 16, 1999


Purpose
Background
System As-Found Condition
Present As-Built
Proposed Modifications/Enhancements
Conclusions



1.0 Purpose

1.1
This report outlines the as-found and as-built condition of the HET glycol system as well as the proposed modifications for enhanced system operation and reliability. The original design requirements for the aforementioned system are published in the HET Technical Report #102, Specification: Telescope Cooler, and will hereafter be referred to as the Report.


2.0 Background

2.1
The design functions of the glycol system are to “… provide a flow of coolant at near ambient temperature for removal of heat from HET electronics and drive motors.” This is to prevent the aforementioned heat from being rejected into the telescope light path.

2.2
The system working fluid is a 40/60% mix of ethylene glycol and water (EGW), respectively.

2.3
The EGW supply temperature at the supply connection is to be within 0.9 °F (0.5°C) of the set point. The Report originally called for a refrigeration unit. No refrigeration unit was installed. An ambient air cooler is installed in place of the refrigeration unit.

2.4
The design pressure limit was not specifically established in the Report; however, a relief valve with a range of 50 to 300-psi was specified. No construction codes or standards for pressure boundary components were invoked by the Report.


3.0 System As-Found Condition

3.1
The pump installed in the glycol system is a positive-displacement triplex-plunger pump that has a capacity of 17-gpm at a maximum head of 2309 feet (1000-psi).

3.2
No mechanical codes or standards were applied or specified in the design of the glycol telescope cooling system; however, the manufacturers of the valves, piping, hoses and tubing did apply industry codes and standards in the design and construction of their respective products.

3.3
The system relief valve capacity was less than the pump capacity and had a maximum set point of 150-psig. During operation of the glycol system, the relief valve was open and acted as a parallel flow path to the telescope. A faulty system valve lineup could have caused a non-passive pressure-boundary failure to occur.

3.4
The pump speed, and hence the pump capacity, is controlled by the output frequency from a variable frequency drive (VFD) motor control system. The motor is a 5-horse power, four-pole, AC squirrel-cage induction motor designed for VFD applications. The VFD is causing considerable noise on to the HET 480-VAC, 60-Hz. Bus.

3.5
The glycol system provides cooling to the tracker’s ten drive motors. The drive motors’ require a flow rate of ½-gpm per motor. The system also provides flow to one coldplate in the FIF electronics box at 1-gpm and to 1 coldplate and 3 transmission oil coolers in the PFIP electronics box at about 0.7-gpm each.

3.6
Heat transfer analysis was performed during the design phase of the tracker to determine the required flow and head pressure required to cool the tracker drive motors. The reported cooling flow required for the tracker drive motors is ½-gpm per motor.

3.7
The coldplate in the FIF electronics box was estimated to require 1-gpm, but no analysis was presented that estimated the cooling flow required for the FIF electronics box.

3.8
The cooling flow requirements for three transmission oil coolers and the coldplate in the PFIP electronics box are not known, and no analysis has been presented that estimates the cooling flow required for the PFIP electronics box.

3.9
The installed flow switch is too sensitive for this application. The slightest flow resets this switch. Additionally, the movement of the dome and shutter cause the flow switch to reset when there is no glycol flow.

3.10
The flow meter is located such that the indicated flow is not necessarily reaching the tracker. There are two bypass valves between the tracker and the flow switch.

3.11
The pressure rating of the flow meter is 250-psig. This is insufficient for the predicted operating conditions.

3.12
The pressure rating for pressure boundary components in the glycol system varies from unknown (estimated to be 250-psi) to 3000-psi. The various system components and their pressure ratings are listed in Table 1 below.


Table 1. Glycol System Component Pressure Ratings
Glycol pump 1000-psi
Flexible hoses 1000-psi to 1250-psi
Drive motor copper cooling coils, 3/16” soft copper. 1935-psi
¼”-Parker Paraflex plastic tubing # NR-4-035 425-psi
Whitey Manual Ball Valves #65TF12 1500-psi
¼”-FNPT Parker Manual Plug Valves #PV609-4 250-psi
Whitey Manual Throttle Valve
P/N B-1RF4
3000-psi
Teel Relief valve #4UN31 300-psi, 25-gpm
Omega Local Flow Meter #FL-7318BK, 0-10 GPM 3000-psi
Remote indicating flow meter, Proteus Ind. M# 260B12F2 250-psi
Hydac Desurger 750-psi
Tobul Accumulator # 2.2AT-1 2500-psi
Various ¼”-NPT Parker CA Series fittings 1400-psi
AAVID Hicontact Coldplate

FIF electronics box coldplate pressure tested to 400-psig.

473-psi. (Appendix A)

See http://tubebook.copper.org/design-data-ratings.html

Automotive Transmission Oil Coolers in PFIP electronics box.

Three units pressure tested to 400-psig.

Unknown pressure rating.

 

Gray PVC pipe fitting at LX Unknown, estimated at 250-psi
OSC manufactured manifold EGW Main 600-psi (Appendix A)
OSC provided manifold Hexapods 466-psi (Appendix A)
Copper pipe for ambient air cooler 364-psi – Type L
Ambient air cooler 300-psi
The above data is vendor provided unless otherwise noted.


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4.0 Present As-Built

4.1
A replacement flow meter has been installed in the glycol system. The meter is located so that the flow it indicates is the flow being delivered to the top of the telescope. This flow meter has a pressure rating of 5000-psi.

4.2
A spare glycol pump has been delivered and installed. The glycol pump that was in-service was leaking and has been rebuilt and placed in spares.

4.3
Throttle valves and flow meters are installed in the return lines to the PFIP coldplate and transmission oil coolers. There is 0.5-gpm flow to the PFIP coldplate and 0.75-gpm flow to the 2 outboard transmission oil coolers. This flow appears to be holding the temperature of the electronics box. An evaluation of the glycol flow required for the Sun station place in the PFIP electronics box was performed and determined that 1-gpm should be sufficient (allows an 8°F temperature rise). The heat load associated with the coldplate is not known.

4.4
The FIF electronics box has a throttle valve and flow meter installed in its return line. Based on the estimated power requirements provided by PSU for the FIF electronics box, 0.4-gpm glycol flow should provide sufficient cooling (Appendix B); however, 1-gpm is currently being provided. Based on operating experience, a flow-rate of 1.0-gpm is more than sufficient cooling flow.

4.5
The as-found relief valve has been replaced with an adequately sized relief valve. The relief valve is set at 300-psig. Currently, with the flow being provided, the discharge pressure of the glycol pump is 260-psig at the pump and 190-psig at the supply manifold on the tracker.

4.6
Three components require replacement/removal in order to achieve a glycol system design pressure rating of 400-psig at 120°F. The flow meter/switch (single component), the PVC item from above and about 60, ¼”-FNPT Parker Manual Plug Valves #PV609-4. These items have a pressure rating of 250-psig.

4.7
The three transmission oil coolers installed in the PFIP electronics box have been pressure tested to 400-psig.

4.8
The coldplate in the FIF electronics box has been pressure tested to 400-psig. Analysis was performed to determine the burst and working pressures for the FIF electronics box coldplate. (Appendix A)

4.9
The coldplate in the PFIP electronics box requires pressure testing to 400-psig. Analysis was performed to determine the burst and working pressures for the PFIF electronics box coldplate

4.10
The glycol pump is operating at 60 hertz providing a flow of 8.12 gpm. This is the maximum flow that can be provided without changing the sheaves on the pump and motor. Sheave changes can be done in less than ½-day should it be required. HET has on hand sheaves that will make available full pump flow capability with the existing motor.

4.11
A new flow switch has been installed. The new flow switch has a range of 4 to 8-gpm and a pressure rating of 400-psig. It is installed in the system so that it will not reset unless the flow resetting it is actually going to the tracker. The new flow switch has been connected to the emergency shutdown system for the telescope. When glycol flow drops below 6-gpm, the switch opens and shuts down the tracker. The new flow switch was installed using red brass male nipples. The burst and working pressure of the aforementioned nipple was determined in Appendix A.


5.0 Proposed Modifications/Enhancements

5.1
A replacement motor has been purchased for the glycol pump. This motor is a 5-horse power, 6-pole motor (880 rpm), sever duty service. Once the final glycol flow is known, this motor can be sheaved and installed. This will eliminate the VFD that is putting unacceptable noise on the HET 460 VAC bus.

5.2
A manual bypass valve will be installed in parallel with the relief valve. This will allow draining of the system for maintenance and provide a manual means of adjusting glycol flow without changing pump speed or sheaving the pump or motor.

5.3
Replacement valves for the ¼”-FNPT Parker Manual Plug Valves #PV609-4 have been ordered. The replacement valves will eliminate 60 mechanical joints in the glycol system up on the tracker. The replacement valves have a pressure rating of 3000-psig. The replacement valves can be rebuilt if required.

5.4
A smaller tank for the glycol system is on hand and can be installed as the glycol system tank. The proposed tank has a capacity of 175-gallons. The existing tank has a capacity of 600-gallons. The advantages of the smaller tank are as follows:

1) reduced surface area to volume ratio with the earth (lower heat gain from the ground)
2) an increased surface area to volume ratio with the air (larger area to reject heat to atmosphere)
3) lower system volume
4) higher suction head to the glycol pump for the same volume

5.5
Using the spare glycol pump mentioned above, install the spare glycol pump and motor for standby service. In this way, no loss of telescope availability will be experienced due to loss of the operating glycol pump. Expansion of the glycol pump house and installation of the requisite piping, valves, and electrical controls are included in the effort required for this modification.

5.6
The new relief valve will be inadequate for the final system configuration. Once the final required flow is known, anticipated to be in excess of 10 to 12-gpm, the discharge pressure during winter ambient conditions is expected to exceed 300-psig. Presently, this is not a problem. The relief valve that is now installed will be suitable for installation on the low-pressure side of the system to protect the ambient air cooler and copper piping.

5.7
A higher set point relief valve of higher quality is required for the high-pressure side of the system. The system relief valve set point will ultimately be 350 to 400-psig. Seat leakage tightness is also required.


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6.0 Conclusions

6.1
Typically, the design specification for a medium energy system such as the glycol system includes the use of industry codes and standards (such as ANSI or ASME) to design the system pressure retaining/boundary components. The manufacturers of various pressure-retaining components such as valves and tubing manufactured their respective components to applicable codes and/or standards. To the maximum extent practical, the system will be back-fit with the design requirements to satisfy a pressure rating of 400-psig per applicable ASME/ANSI codes and standards.

6.2
It should be noted that positive displacement pumps provide the head required, up to and including non-passive failure of the pressure boundary or an electrical fault, to deliver the flow defined by the pump operating speed. In other words, the pump head versus flow curve for a given operating speed is a vertical line; therefore, an adequately designed relief valve is essential to preclude system damage due to an improper system valve lineup. Further, the system must be designed in accordance with adequate codes and standards to ensure system structural integrity and the protection of personnel and equipment over the operating life of the system.

6.3
The glycol system is being used to cool electronics boxes. Since glycol is provided at ambient outside air temperature, it is assumed that the electronics within the boxes cooled by the glycol system are sufficiently robust to withstand summer nighttime ambient air temperature as their heat sink temperature. Based on ASHRAE Fundamentals (El Paso data), 1997, this temperature can be expected to be as high as 80°F or higher. Based on review of local weather data, the ambient temperature at the beginning of observations could be as high as 90°F. Under the aforementioned conditions, the temperature within the boxes may be as high as 95°F to 100°F depending on the efficiency of the airside of the coolers used. This should be considered in the design of electronics to be cooled by the glycol system.

6.4
The pressure rating for the glycol system is 400-psig. This should be considered a design-input for equipment that is added to the telescope if it is to be cooled by glycol.

6.5
The air cooler pressure rating is 300-psig, and the copper piping connecting it is rated to 364-psig. This part of the system is on the low-pressure side of the system and will require a separate relief valve.


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Last updated: 01-Oct-2003

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