Month: January 2019

Jesse Grandbois is one of the techs who reads the tech tips and he wrote a few tips that he wanted to share on some gas furnace control basics. This tip is about the basic terminal designations on typical 24v gas valve. Thanks Jesse!


Have you ever noticed the TH / TR terminal on a gas valve?. When I was in school, I’ll admit I didn’t know what it was. I’ve worked with people that are experienced and still think you need to use it. 
 
Nobody ever explained to me what it was. Being a newbie at the time it never clicked when I looked at the wiring diagrams. All my teachers would give the same response, “it’s a common.” 
 
That’s where the confusion set in. It’s a common. We throw this word around like it’s going out of style it seems in the HVAC industry. Everything is a “common” and technically a common is just a “common” point of connection but it really doesn’t clear up it’s intended purpose, or what part of the circuit it is intended for.
 
Following the diagram below while reading the rest of the article should clear things up.
Lets look at what each of these terminals mean:
TH – The 24v hot leg from the thermostat on a call for heat (R+W closing) to the gas valve (TH terminal) to open the solenoid to allow gas to flow. This is assuming the transformer is good and the high limit is closed.
TR – The 24v common/return side of the transformer.
TH/TR – This is not internally wired to the gas valve. Not using this makes no difference to the circuit. You could run your 24v hot from the transformer directly to your NC high limit in the above example and be just fine. This is nothing more than a convenience terminal. Joining these wires with a marette (Wire nut or terminal multiplier) does the same thing as this terminal.
Hope this helps clear up any confusion.
— Jesse

This article is written by up and coming young tech and new contributor Kaleb Saleeby. Thanks Kaleb!


Recently, I came across a work order description in my dispatch that made me scratch my head.


“Clean Salamander broiler”

I had to ask the omniscient Google for answers. Turns out, it has nothing to do with vividly-colored, “fireproof” amphibious creatures! The name does, however, pay homage to 17th-century lore that salamanders could withstand the heat of a fire, and were even believed to come from fire itself.

    

None of this information aided me in understanding how to clean this particular type of open-air broiler, so I did more research on how the appliance was constructed, and how it operates. From my findings, the overhead broiler is a very simple design. The basic components of a gas salamander broiler are as follows:

  • Gas valve

  • Gas manifold

  • Fuel orifice

  • Distributor

  • Igniter

  • Burner

  • Food racks

    

The gas valve on the appliance I worked on was quite literally just a knob the client manually turned on or off. When open, the gas valve allows a set fuel pressure through the manifold to be fed out a single orifice, which then gets fed through the burner. The gas is spread through the burner via a distributor to feed the ceramic plates at the end of the burner. The igniter would be the next in this sequence of operations; however, the appliance I worked on did not have a functioning igniter, and the client refused replacement, resulting in manual lighting. The ceramic plates of the burner are littered with tiny holes that allow the flame to burn uniformly across the burner with little to no major fluctuation.

    

None of my research gave me any answers on how to clean this equipment. I reached out to Refrigeration Technologies’ Chief Executive Officer and Founder, John Pastorello for advice on what chemicals, if any, he recommended for this job. According to John, Viper HD cleaner is safe and appropriate for the cleaning of this type of broiler. Viper HD is a slightly alkaline (basically neutral on the PH scale) cleaner that will not damage the fragile ceramic burner, as long as it gets rinsed. John states,

 

“You will need Viper HD and a scrub brush. As long as you rinse you will not have a problem with the heating elements. On stainless [steel], you can use HD with a soft scrub. Rinse then use a stainless steel cleaner to finish. The [stainless steel cleaner] will have a mineral oil that leaves a finger proof coating and brings out the luster. This is a labor [intensive] job because of the heavily carbonaceous soil.”

    

The cleaning of the appliance was fairly simple, albeit frustrating. The grease and grime were the hardest part. Once everything was clean and dry, I reassembled the appliance and relit the burner. After a few minutes of allowing the flame to stabilize, the appliance was operating well and to the satisfaction of the client.

    

In retrospect, I probably would avoid forcing water into the burner section. The burner assembly I worked on was riveted together, and did not allow access to the inside. I have since learned that there is insulation on the inside of the burner assembly, and wetting the insulation can potentially cause issues with the equipment, even if it has been dried off. I would recommend anyone else who encounters a job like this to use a Viper HD saturated towel and wipe the ceramic burner to clean it, and then rinse with a water-damp towel. I would also recommend focusing on the distributor inside the burner, as it may be heavily caked with carbon buildup. All other steps would remain the same. I also learned that there are overhead broiler models that have a burner design that does allow you to change the ceramic plates and insulation, if necessary, to make the cleaning process easier.

    

I hope this helps other guys, like me, who may get sent to do hot side service. It certainly is interesting!

– Kaleb

Citations

Dissimilar metals, like Aluminum, Copper, Brass, and Steel are some of the main metals one may experience in their trade and few are comfortable working with. They don’t trust their brazed joint, or they are afraid of melting away material. To put some of the nerves of those in the field at ease let’s understand our metals with a specific focus on thermal effects on structures of metals.

 

To review the extreme, we theoretically come upon a copper and aluminum joint. The plan is to braze the two together with my copper being my male and the swaged aluminum as my female. I find an applicable alloy and bam!!! Would you look at that nice joint, I quickly cool the joint off by applying a wet rag to it, then tug on both ends which separates the two Alloys completely.

 

What the Flux!!! Only thing I can think of that I did not do was clean my joining metals.

 

Our issue here goes much deeper than a proper cleaning.

 

Thermal Expansion Coefficient of:Thermal Expansion (Microinch per °F)
Aluminum13.1
Brass10.4
Copper9.8
Steel7.3

Iron

6.8

Each material has a different response to the heat, which is characterized by its thermal expansion coefficient. The thermal expansion coefficient represents the amount that the material expands per each degree increase.  It is important to know that whatever the solid expands when heated it also contracts when cooled, but not necessarily at the same rate of expansion.

 

Each time you are cycling through expansion and contraction you are altering the structure of the metal as well as reducing its ductility or ability to flex without becoming brittle.

 

What should we consider when working with two different (Dissimilar) metals?

  • Melting temp of brazing alloy and brazing metal
  • Metal thickness
  • Brazing Metal Ductility
  • Heating and cooling rate of joint
  • The heating rate of the torch being used
  • Galvanic Corrosion between the two dissimilar metals
  • Oxidation of the metals heated

Referencing Copper to Aluminum, the vastly different thermal expansion rates of two metals make this joint very difficult to make.  When joining the two, we would use a brazing alloy that has a fluid melting temperature below our brazing metal as we want our brazing alloy to be pulled and filled into our joint through capillary action. The alloy must also be ductile enough to maintain the bond throughout the expected temperature range of the joint while in service.

Without the proper clearance between the aluminum and the copper, there is no guarantee that the brazing alloy will properly fill the joint and create a trustworthy bond and when working with dissimilar metals you will generally want to allow the work to cool naturally rather than cooling instantaneously with water.

— Sal Hamidi w/ Productsbypros.com


If you ever sat close to a bonfire on a really cold night, you may have noticed that your face starts to get really warm. The minute you put your hands up and shield your face from the light of the flame your face cools off almost immediately.

This happens because the flame is heating your face through THERMAL RADIATION not by heating the air in between.

Many have taught that radiant heating (thermal radiation) happens when one body of matter is exposed to a light source such as the sun or a fire. While this is partly true, the VISIBLE light spectrum is only a small part of the story.

Take a look at this photo above taken using a Testo thermal imaging camera. This image could have been taken in complete darkness and yet it displays the thermal radiation.

This is because EVERYTHING that is above absolute zero puts off thermal radiation in the form of electromagnetic radiation, because everything in our world is above absolute zero (-460°F) everything emits radiant heat.

In the case of the human body, we are putting off radiant heat to everything around us as well as picking up radiant heat from all of those same objects. The net thermal (heat) effect on our body is based on whether the average surface temperatures we are exposed to are higher or lower than our body temperature.

Thermal radiation can be “reflected” in the same way as visible light. This is why these weird “space blankets” can keep a person warm by simply reflecting back their own thermal radiation.

The real world effect of thermal radiation on heat load and human comfort are huge.

You can have a room with an air temperature at a comfortable 72° that can still feel hot or cold to an occupant based on the temperature of the surfaces around them. In fact, studies have shown that the wall surface temperature has the same effect on comfort as room air temperature.

A 1°F change in wall surface temperature is nearly equal to a 1°F change in air temperature as it relates to overall thermal gains/losses to the human body.

This shows that why radiant cooling and heating and products like radiant barriers make such a big difference.

It also makes a difference in cases of thermostat and sensor placement. It isn’t just a matter of keeping the thermostat or sensor out of the sun, you must also consider what objects the sensor is “exposed” to through line of site thermal radiation.

— Bryan

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