ASHRAE-CFL » Refrigeration

Refrigeration Tour Recap (5/14)

jalphonso — Sat, 14 May 2011 23:08:50 +0000

Thank you one and all who attended the ASHRAE Refrigeration Tour 2011. A group of about 15 ASHRAE members toured Bari Beef International (BBI) on May 6, 2011. BBI has been providing quality meat products in the Central Florida market since 1985. Their new USDA processing center, a 74,000 square foot facility is comprised of state of the art technology along with some time honored traditional methods.

Colin Mclean (CEO, BBI) gave us a tour of his facility. This facility holds about $ 5 million inventory at one given time. Our technical tour guides, Jim Grady and Dean Ellerbrock answered some of the technical questions. Jim and Dean combined have over 75 years experience in the refrigeration industry.

Key elements of a refrigerated warehouse design were discussed. The group had good questions about operating costs, especially the cost of energy. Colin pointed out the different processes involved in the aging of meat, especially the special “dry aging” process. This type of aging involves tight temperature and humidity control which imparts a very palatable and unique taste to the meat.

We thank Colin and BBI for opening their doors to our ASHRAE group. Also, a special thanks to Paul Halyard, P.E and the staff at University Club for their assistance in setting up this tour.

- Jason Alphonso, Refrigeration Chair, 2010-2011

Not-So-SILENT “R” – Q#1 (3/4)

jalphonso — Fri, 04 Mar 2011 19:00:50 +0000

We have a winner !

Taner Tekin
March 8th, 2011 at 5:25 pm

CONGRATULATIONS !

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Goal -

To create awareness about refrigeration and have fun along the way !

Rules –

1.The scenario below is completely fictitious and is to be used for numerical analysis only.

2.Not 100% sure of your answer? You can use a fictitious name or initials in the comment section. Please be sure to provide your correct email address. We will need that information to contact the winning entry. Your email address will not be posted. All comments will be time and date stamped.

3.Do NOT provide any calculations. As an EXAMPLE only, the answer to the quiz below needs to be in this format

YES, 1.0 kW/ton

4. You could make as many attempts as you like.

5. Prize – Free dinner at our next technical meeting. Good luck!

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Quiz –

The COP of a household refrigerator is 3.2 and works on a simple vapor compression cycle. The total cooling effect is approximately 3 TOR (36,000 BTUH). Government regulations require these refrigerators to be more energy efficient than 1kW/ton.

1. Would this refrigerator qualify (Yes /No)?
2. What is the kW/ton rating for this refrigerator?

Please leave your answer in the form of a comment below.

Refrigeration – Interview with an ASHRAE Refrigeration Expert ! (2/9)

jalphonso — Thu, 10 Feb 2011 10:44:52 +0000

We had an email with an ASHRAE Refrigeration giant at the ASHRAE Winter Meeting in Las Vegas, NV. Roberto Aguilo has worked on a host of ASHRAE refrigeration committees and is nominated (to be confirmed by election before July 1, 2011)to be Director at Large (DAL) to the ASHRAE Board of Directors . He comes to ASHRAE from Buenos Aires, Argentina.

Name: Roberto Aguilo

Title/Committees:

Research Administration Committee (RAC) – Liaison Section 10 (All TC’s of Refrigeration)

Alternate Region Chair (ARC) – Region XII
Refrigeration Handbook Committee – 2 terms

Incoming Director at Large (DAL) – ASHRAE Board of Directors.

1. Tell us about your committee.

RAC is responsible to manage the funds for research projects. We have to revise and qualify the proposals and select the institution/person responsible for certain a research project.
2. I have heard the phrase “ASHRAE with the Silent R”. Is that true? Do you think ASHRAE could do more for refrigeration?

The “R” in ASHRAE is not silent. Despite it is not one of the maximum priorities of our society a lot of people work on issues related with it. As always we can do more, and we are working to improve the research and the publication of documents and books about refrigeration.

3. List 3 of the hottest topics in refrigeration today .

Systems with C02

Improved heat transfer (technologies like microchannel heat exchangers)

Variable capacity compressors

4. Which single word / technology will be the refrigeration buzzword in 2020?

I am not sure about the meaning of buzzword, but my answer is energy efficiency in refrigeration installations.

5. Have you been to the EXPO? What refrigeration technology caught your eye?

I have no time to go to the exhibition

Thank you Roberto. We are proud you represent Region XII and wish you the very best in you ASHRAE responsibilities, especially your DAL position beginning July 1, 2011.

- By,Jason Alphonso – Refrigeration Chair, 2010-2011

Refrigeration – Addendum “ak” to ASHRAE Standard 34-2007 (12/7)

jalphonso — Tue, 07 Dec 2010 23:13:22 +0000

In a previous Dewpoint article we talked about flammability in the broad sense of refrigerant safety. We understood various classifications with an increasing numeric denoting higher flammability i.e. A refrigerant classified A3 has higher flammability than say A1. ASHRAE standard 34-2007 has come out with a new Addendum ak adds a new line item to the classification.

This addition is of a new 2L subclass to the existing class 2. This was driven by flammability as a main safety concern. Examples of some of the refrigerants in this new classification are R-1234yf, R-1234ze and R-32. They are commonly being referred to as “A2L Fluids”.

Revision to ASHRAE Standard 15-2007 (Safety Standard for Refrigeration Systems) based on 2L classifications are still under negotiations.

The article was adapted from the ASHRAE Journal – October 2010 edition and co-authored by Jason Alphonso, PE

By, Cameron Sherwood– Refrigeration Chair, 2010-2011

Refrigerant Safety – Your car’s refrigerant in 2013 ? (10/3)

jalphonso — Sun, 03 Oct 2010 15:35:28 +0000

On the critical topic of life safety, choice of refrigerant is a very important consideration a designer should be very cognizant about. ASHRAE Standard 15-2004 duly assigns two character alpha-numeric designations to denote refrigerant safety. Two characters make up this designation – an alphabet denoting increasing level of toxicity (A or B) and a number denoting increasing flammability (1, 2 or 3). That being said, a refrigerant labeled B3 according to this standard would imply high toxicity and flammability. This refrigerant, if used, would require additional consideration in mechanical system design.

On the topic of refrigerant safety, how important would refrigerant choice be in the car you drive every day? The September 2010 ASHRAE Journal reported that American automaker General Motors will now use a new refrigerant HFO-1234yf as a replacement to HFC-134a. This will happen in all GM models beginning 2013. As it turns out, refrigerant safety is a given here; the actual driver was not safety, but global warming potential. It was reported that HFC-134a stays in the atmosphere for the whole of 13 years, but HFO-1234yf a mere 11 days. Does this mean an immediate end to the pollutant? Not so fast according to the US based Society of Automotive Engineers (SAE), which says HCF-134a is not going away anytime soon. This is because HFO-1234yf is not a direct refrigerant replacement and HFC -134a will still be needed to service existing vehicles.

More importantly the US EPA still needs to certify it as non-toxic. Therefore pending approval, you can rest assure your new GM 2013 car will be doing a good job protecting our planet.

By, Cameron Sherwood– CTTC Refrigeration Chair, 2010-2011

Water Cooled Chillers – Open or Hermetic Drive—Part 2

mtosh — Mon, 01 Mar 2010 11:27:35 +0000

By: Cameron Sherwood

Last month I explored two options for motors for water cooled chillers. Here is a scenario to think about and determine which configuration is best for a project design.

An open drive 1350 ton machine will dissipate approximately 123,175 btuh to the mechanical space (according to manufacturer data). If three chillers are required for the project that is about 31 tons of cooling and about 19 tons for associated pumps and cooling tower pumps (according to some manufacturers). This is a combined cooling load of about of 50 tons of cooling load to maintain a space temperature of 80°F (from manufacturer data). To meet cooling load with an open drive chiller, a larger air handler and associated equipment would be required. With a hermetic drive chiller the 31 tons of motor heat would be transferred to the condenser water via the refrigerant, thus reducing chiller capacity. In either case, chiller motor heat reduces chiller capacity; heat is created and needs to be transferred. A task accomplished by air or liquid.

Based on my career in the Navy while operating, repairing, and maintaining several machines that would operate in extreme conditions, the open drive and the hermetic drive units are comparable from a reliability standpoint. Some of the conditions I’ve seen are: entering condenser water of 100° F, setting the capacity controls to 110%, start and stop a machine several times an hour (more than manufacturer recommendation), constant power fluctuation, mechanical space temperatures of 120° F, and anything else that manufacturers do not recommend. With the machines operating for several years in extreme conditions, there were no electrical motor failures or major mechanical failures. Minor failures included: open drive machine compressor shaft mechanical seals would fail and refrigerant would leak, allowing air and moisture into the refrigerant system, valves or other moving parts would freeze, and acid would be created, causing damage to the internal parts of the system. Due to power loss and fluctuation electronic control boards would fail.

Facilities owners will have manufacturer preferences, but a knowledgeable engineer can guide the owner to a more informed decision.

Water Cooled Chillers – Open or Hermetic Drive

mtosh — Wed, 27 Jan 2010 15:05:42 +0000

By: Cameron Sherwood

There are two options for motors for water cooled chillers, Open Drive and Hermetic Drive. An open drive has an electric motor that is air cooled by the ambient air. A hermetic drive has an electric motor that is hermetically sealed and cooled with refrigerant. With having experience repairing and maintaining both open drive and hermetic drive machines, each arrangement has its advantages and disadvantages.

Open drive water cooled chillers have the possibility to be driven by other means such as steam turbine, gas motor, or gas turbine, etc. These machines can be converted to alternative refrigerants; the motors do not rely on refrigerant for cooling. Open drive electrical motors can have electrical power diversity, capable of handling high voltages, which will reduce a facilities transformer needs. The electrical motor will have more windings, though, due to higher operating temperatures thus adding motor heat to the space. Repairs can be made to the electrical motor since the motor is accessible. There is a mechanical seal for the compressor shaft that connects to the motor shaft, this mechanical seal will leak in due time. This, as we have all experienced, is in line with the old quote, “More moving parts and more points of connections creates the possibility of more probable failures in time.”

Hermetic drive chillers have electrical motors that are cooled with refrigerant; this allows for reduced motor winding and minimal heat dissipated to the space. The electrical motor heat will be transferred from the refrigerant to the condenser water. Hermetic drive chillers do not have shaft coupling of the motor to the compressor or mechanical seal, which creates a lesser chance for failure. These chillers have placement versatility, i.e. they can be placed outdoors, because the motor is sealed and not cooled by ambient temperatures.

Critical Environment DX Systems and SST

mtosh — Sun, 01 Nov 2009 21:42:40 +0000

By: Cameron Sherwood

Sometimes for an Operating Room (a second coil or a packaged DX for a mobile unit hospital) a commercial Split DX System with a Constant Volume Draw-Thru AHU and matching condensing unit will require a 49° F LAT off the coil to maintain space temperature and humidity, the system must operate continuously with no fluctuation. The biggest concern is to avoid coil freeze up from a low SST, dirty coil, clogged condensate drain, or coil restriction. When ice begins to form it can take several hours to thaw, and could trip the fan motor due to high static. Low suction pressure will cycle the compressor off; it will take a minimum of five minutes to restart the compressor, which is unacceptable if a surgery is in progress. To avoid coil ice up, SST must be controlled.

Saturated suction temperature is the temperature of the refrigerant when it is 100% vapor at the specified pressure. Any increase in the temperature to the vapor will result in a super heated state. Super heat ensures no liquid refrigerant will be circulated back to the compressor, avoiding damage to the compressor. The industry standard is 8° F to 12° F of super heat.

Liquid refrigerant is metered through the coil by a Thermal expansion valve (TXV) or capillary tube(s), the metering device is the dividing point between the high-pressure and the low pressure side of the system. The refrigerant leaving the metering device is about 75% liquid and 25% gas. Liquid refrigerant will boil off approximately 90% of the way through the coil; reaching saturated vapor (saturated suction temperature).

Refrigerant has a temperature pressure relationship, meaning that at a specified pressure it will correspond to a specific temperature, any temperature above that is super heated vapor, and any temperature below that is sub-cooled liquid. To calculate super heat the suction pressure must be known and the actual temperature of the suction line must be known, the closer to the coil, the more accurate, for example, R-22 at 68.51 PSIG has a saturated vapor temperature of 40° F, per the chart, but actual suction line temperature is measured at 50° F, thus yielding 10° of superheat.

In a low load condition the TXV will throttle down, reducing the suction pressure and correspondingly the SST will also decrease. Many publications indicate that with a SST of 38° F ice begins to form, this will create a low suction pressure, the compressor will cycle off or hot gas by-pass will initiate, thus a fluctuation in temperature and humidity will occur. To prevent this some manufacturers recommend a SST of 40° F – 43° F for a Constant-Volume AHU. For critical applications where cooling cannot cycle or have temperature fluctuation, having a SST less than 40° F SST creates an undesired risk, even when utilizing a defrost cycle.

Split DX Systems and SST

mtosh — Tue, 01 Sep 2009 17:26:00 +0000

By: Cameron Sherwood

When selecting a commercial split DX system with a constant volume draw-thru AHU and matching condensing unit for low supply air temperature (SAT) applications, the saturated suction temperature (SST) is a concern. The SST is the temperature of the refrigerant inside the cooling coil, so we assume the cooling coil will be the same temperature. Ice begins to form on the cooling coil with a SST of 38° F; any lower temperatures are not advisable. To prevent the coil from icing and to have some leniency for fluctuation in the system and/or design, some manufacturers recommend a SST no less than 41° F.

A DX AHU selection for the design CFM may yield a SST less than 41° F when the LAT off the cooling coil will be 49° F with a SAT of 52° F; these are low temperatures and run the risk of freezing the coil. One solution to increase the SST to 41 ° F can be achieved by increasing the air flow, preventing the coil from freezing, and the extra air can be distributed to non-vital areas. This is not the most energy efficient method, but it will keep the initial cost down when price is an issue. Utilizing energy recovery equipment or desiccant wheels to reduce the cooling load on the DX coil is also an option.

Refrigerant capacity control is important to maintain adequate SST. Capacity control allows the unit to operate, maintain space temperature and humidity by avoiding short cycling during low load conditions and prevent icing of the coil. Hot gas by-pass or variable volume compressors are appropriate control strategies.

Chiller Head Pressure Control

mtosh — Sun, 02 Aug 2009 01:08:56 +0000

by: Cameron Sherwood

Chiller condensers can be controlled by the industry standard of condenser water temperature, which are 85° F inlet and 95° F outlet. This is the easiest and most cost effective, but not the most effective method for controlling a chiller condenser. By controlling the condenser water temperature, the chiller is not being directly controlled; meaning the condenser pressure (head pressure) can vary. The chiller can run more efficiently if the chiller head pressure is controlled by modulating condenser water flow to achieve optimal condenser pressure. Controlling the chiller condenser head pressure to operate at the lowest head pressure suggested by the manufacturer, the optimal Delta-Pressure across the compressor discharge to the suction is maintained, thus increasing efficiency.

Controlling a chiller head pressure can be achieved by a water regulating valve (WRV), VFD driven pump, or both in tandem. The WRV should be installed on the water side of the condenser barrel discharge to ensure the condenser barrel will be filled 100% with water. The condenser head pressure can be controlled by two different methods. The first method is the WRV or VFD driven pump, it will receive control signals from a transducer; the transducer receives a signal from a sensor mounted in the refrigerant side of the condenser barrel. The second and most common method is the WRV, it will receive control signals from the condenser barrel refrigerant gas pressure (head pressure). This is accomplished by a copper tube being brazed into the refrigerant side of the condenser barrel and routed to the WRV actuator. Both methods operate as the condenser refrigerant pressure increases or decreases the signal to the actuator will also increase or decrease, modulating the water flow to maintain the head pressure set point. The condenser water system can be designed as a variable-primary (for dedicated single pump single chiller arrangement or headered pumps to multiple chillers) arrangement or a constant volume system. By controlling the chiller head pressure the chiller is operating at peak performance.