Keeping Your Cool!

Hot weather is coming, and that can mean slow refrigerant recovery. It is common to have high recovery tank temperatures and pressures shut you down as the temperature rises. The condensing temperature of the refrigerant in the recovery unit has to be higher than the outside temperature, and so the refrigerant leaving the recovery unit can be hot, especially on a hot day. This raises the recovery cylinder temperature and pressure, which in turn makes the pressure leaving the recovery unit climb even higher since it must be higher than the cylinder pressure. You often need to cool the recovery cylinder to keep going. There is the old stand-by: ice and a bucket. It works great, but involves the extra bother of carrying ice and a large bucket to the job site. You can use the recovery machine to cool off the cylinder.

Connect the vapor valve of the cylinder to the inlet of the recovery unit and the liquid valve of the recovery cylinder to the outlet of the recovery cylinder. Purge both hoses of air. Start the recovery unit with both cylinder valves open. After the unit gets started, turn the liquid valve on the recovery cylinder clockwise to create a restriction. Be careful NOT to completely close it off. You have just made a refrigeration system with the refrigerant recovery cylinder acting like a flooded evaporator.

The recovery unit is provides the compressor and condenser, and the partially closed liquid valve on the cylinder acts like a metering device. Liquid in the cylinder boils as vapor leaves, cooling off the remaining liquid. The returning liquid is at a lower pressure and temperature, thanks to heat being removed by the recovery unit and the pressure drop at the liquid valve. It takes a bit of practice to learn where to set the liquid valve, but you can monitor the two pressures on the gauges of the recovery unit. You should see both pressures drop as the unit operates.

I have made cylinders frost on the bottom using this technique. One caveat – if you wait until the high pressure switch on the recovery unit opens, you can’t use this method to cool the cylinder down since the recovery unit won't run at that point. You need to make sure and cool the cylinder before that happens. One manufacturer used to make a recovery unit with this feature built in. You connected two lines from the recovery unit to the cylinder, and anytime you needed to cool the cylinder down you would just set the recovery unit valves to subcool. This kept you from having to move your hose connections after the cylinder was cooled down. However, I don’t think it is available any more.

Tape is Tape NOT!

I must admit that when Glenn Walter of Shurtape offered to do a presentation on duct tape application for my class I thought “Oh HOW exciting!” (Yawn) After all, how much can there be to know about duct tape? It can’t even connect to the internet! But then I really hate to turn away help and I like having people from the industry come talk to my students, so we set up a class. One thing I have come to understand about life in general: whenever I think there is nothing to know about a particular subject, it is only because I know so little I don’t understand how ignorant I truly am. When Glen started his presentation I quickly realized that there is whole lot to know about duct tape. What follows is a cliff notes version.

Duct tape consists of a backing and an adhesive joined together. There are four types of backing: cloth (the old standard), film, foil, and foil-skrim-kraft (FSK).  There are two large categories of adhesives: acrylic and rubber based. Most techs know that codes require UL 181 tape. However, did you know that there are two general categories of UL 181 tape: 181-AP and 181-FX.  AP is rated for use on rigid ductboard and FX is rated for use with flex. Note that there is no specific UL rating for tape on metal duct systems – UL 181 is for ducts made out of manufactured materials. You may have also seen tape with a UL 723 rating, which is a smoke and flame spread standard. It makes a difference WHICH UL rating your tape has. Just because you see UL does NOT necessarily mean your tape is correct for the job. Even two tapes with the same UL rating can have different application specifics. Also note that the UL rating is not based on the backing or adhesive, but the tape performance in specific tests. Shurtape has 181-FX tapes with foil, film, and cloth backing with both acrylic and rubber adhesive. They are all approved for use with flex duct, but each has a specific application where it is better. For example Shurtape’s film backed tape with acrylic adhesive is rated for application between -20°F and 220°F. Their other FX rated tapes won’t stick at -20°F.

Most codes now require mastic for sealing metal ducts, but many people still use tape underneath the mastic. Did you know that many duct tapes are not rated for that use? Mastic does not stick well to film tapes. Not all cloth tapes play well with mastic because the chemicals in the mastic and the chemicals in the tape adhesive may not be compatible. The cloth tape might turn loose, then having the tape underneath the mastic just creates a place where mastic is not fully adhered to the duct. Foil tape usually does fine under mastic.  You should check with the tape manufacturer before using a tape underneath mastic.

Finally, the tape application is not complete until you apply pressure. For foil backed tapes, a plastic tool with a stiff rounded edge is preferable for working the tape into the duct. The pressure is needed to fully activate the adhesive on the tape. The adhesive undergoes a chemical process, similar to glue setting. Duct tape is not fully adhered until this process has been started through pressure application and completed with time. Believe me, there is a LOT to know about duct tape. If you would like to learn more, contact Glenn Walter of Shurtape at gwalter@shurtape.com

Bluetooth Tools for HVAC

At the recent HVAC Excellence Instructor’s Conference there were many digital tools featuring Bluetooth connectivity on display. These tools allow you to use phone and tablet apps which take readings from the device as input. This can be as simple as just displaying a reading, or more helpful such as using the reading to perform a calculation. Most also allow the user to use their phone or tablet to send the information to someone else. Technicians can send real time readings to a service manager for consultations or document results to verify system operation. Most of the devices were measuring pressure and temperature. Of course, the Stride i-manifold was there. It was actually introduced last year. This year they have company. Fieldpiece has had wireless gauges longer than anyone else, but they used a proprietary signal. This year Fieldpiece was showing a set of digital gauges with Bluetooth and a Bluetooth wireless bridge to allow their older Fieldpiece wireless gauges to connect to Bluetooth.

 Yellow Jacket, Appion, and Sporlan all had pressure and temperature measurement tools which featured Bluetooth connectivity and apps designed to work with the tools. To be sure these are not manifolds, but pressure and temperature measurement tools. Appion had a trio of pressure gauges and a Vacuum gauge. Their gauges each have a digital display as well as sending Bluetooth information to your phone. They are “short” gauges with a short stem, allowing connection without filling a set of hoses with refrigerant. The Yellow Jacket Mantooth device is also a “short” gauge, but it has no display. Like the i-manifold, it relies on your phone or tablet for a display. The Mantooth consists of a digital pressure gauge with a tethered temperature clamp. Sporlan was showing off a set of digital pressure and temperature devices with Bluetooth connectivity. They also rely on the connected device for a display. 

All Bluetooth devices were not gauges - Fluke and UEI were showing Bluetooth enabled digital multi-meters and clamp amp meters. 

All these devices were showing apps designed to work with the device and extend its usefulness. Most can be freely downloaded. The i-manifold app is a killer app that is useful even if you don’t have an i-manifold. The Stride folks are hoping you will get tired of typing in the pressures and temperatures and pick up an i-manifold. One final consideration – If your gauges, multi-meter, thermometers, and vacuum gauge are all connecting to your phone while you work, you are going to need some extra juice to keep operating. You will need an extra battery pack or two for your phone, most phones won’t operate all day long without a recharge.