Saturday, January 7, 2017

CSST Gas Lines

If you use flexible gas connectors or CSST (corrugated stainless steel tubing) when hooking up the gas to a gas appliance, you need to make sure and do it safely. Flexible gas connectors are made of corrugated stainless steel and generally have no outer covering or protection. They are often used to connect a gas appliance to a rigid iron gas line. 

CSST, on the other hand, has an outer covering over the corrugated stainless steel, comes in large rolls, and is often used instead of black iron when piping gas lines. There are some installation practices for each of these products that need to be followed to avoid setting up a dangerous situation.

For flexible connectors, it is important that they not be used to go through walls, floors, or the unit cabinet. Iron pipe should pass through the unit cabinet to the gas valve. Contact with the metal side of the furnace cabinet can rub a hole in a flexible connector. Another reason for keeping flexible connectors out of the cabinet is the potential for loose electrical wires or connections to arc against the flexible connector and blow a hole in it. While this could also happen with black iron, there is far less likelihood of the arc blasting a hole in the iron. 

Flexible connectors can be used to make the final connection between the black iron leaving the furnace cabinet and the black iron piped into the furnace area. When using a flexible connector, the flared connectors are generally considered “unions.” Don’t forget to install a gas shutoff. Some flexible connectors are provided with a gas shutoff.

CSST is similar to flex connectors in construction with an outer layer of protective plastic. CSST can be pulled through interior walls, but metal nail protectors are required anywhere the CSST is inside the wall. CSST manufacturers make striker plates for this purpose. Protection needs to be approved by a listing agency, such as CSA or UL. Also, it is still best to use black iron to go into the furnace cabinet. The best practice is to penetrate exterior walls with black iron. If CSST is used to penetrate an exterior wall, protection is required.

One of the biggest safety concerns with both flexible connectors and CSST piping is properly grounding the gas piping system. There have been many instances where lightning strikes near a building have blown holes in CSST gas lines or connectors. The grounding is to avoid this. The most common practice is to connect a bonding ground wire to the rigid black iron pipe outside the house BEFORE the first CSST connection. This bonding ground is connected to the ground rod or run inside to the ground bus of the electrical panel.

Here are a couple of links for more information”


Monday, January 2, 2017

Don't Forget the V

I recently spent some time in Hawaii and noticed that many buildings, both residential and commercial, had no heating or cooling systems. Instead, many only had provisions for ventilation. You see, the temperature in Hawaii rarely gets too far out of the comfort zone, so they condition through ventilation. Now to be sure, there were certainly times when I wished where I was staying at least had a dehumidifier, but the temperature was never an issue. Larger commercial buildings did have air conditioning, but smaller stores usually did not. All  buildings had lots of provision for letting the outside air in.
Hawaiian Air Conditioning

In talking about HVAC we often forget to spend any time discussing the V – ventilation. Even if your building has heating and air conditioning, some amount of ventilation is necessary to maintain healthy comfort conditions. The more people and activities you have inside, the more ventilation you need. Most commercial buildings with large central ducted systems have the ventilation built into the duct system. Another common arrangement is to have a dedicated ventilation system whose only purpose is to pull in ventilation air from outside and expel stale air from inside. These systems are often used for buildings which do not have centrally ducted systems. For example, a building which uses VRF systems to heat and cool often have dedicated ventilation systems.

For years residential buildings have depended upon infiltration to provide ventilation. With increasingly tight houses, this method is becoming unworkable. Even for leaky houses this is far from ideal because  you don’t have any control over how much “fresh” air leaks into your house, or where it is coming from. Some may be coming in through your fireplace or crawlspace. In that case, it may not be very “fresh.”

Residential ventilation systems are now available that allow you to control the amount of outside air entering your house. By adding the outside air into your duct system, you can also control where it enters. Another benefit to adding outside air purposefully with a ventilation system is that it can be filtered and conditioned before entering the living space. I encourage you to think a little more about the V in HVAC. You might find it to be a breath of fresh air.

Sunday, December 18, 2016

Refrigerant Line Sizing

Refrigerant line sizing is an overlooked aspect of system application and installation. Incorrectly sized refrigerant lines can rob your system of capacity and reduce its efficiency. In a worst case scenario, incorrectly sized and applied refrigeration lines can cause multiple compressor failures. For most applications, the two lines involved are the liquid line and the suction line. 

Pressure drop in the liquid line can create flash gas in the line before the refrigerant reaches the metering device. This causes a drop in system capacity because it reduces the amount of liquid entering the evaporator. Some pressure drop is inevitable. It is important to have enough liquid subcooling to offset the pressure drop through the liquid line. 

Suction line pressure drop also hurts the system performance by increases the compression ratio and reducing the amount of refrigerant being circulated. The general rule is to try and keep suction line pressure drop below an equivalent saturation temperature drop of 2F. The actual amount of pressure this represents depends on the refrigerant and the evaporator saturation temperature. Suction lines have another very important design criteria: the refrigerant traveling through them must have sufficient velocity to return oil. While larger lines help reduce pressure drop, they also decrease refrigerant velocity. In general, you want your suction line to be as large as possible while still having enough velocity to return oil. 

There are far too many variables to mention in a blog post, but I can point you toward some excellent materials available online. DuPont and Lennox both have excellent refrigerant piping handbooks available on the web in pdf form. The Dupont document is applicable to all forms of refrigeration while the Lennox material is primarily for air conditioning. Virginia Air has a great excel file which does a lot of the heavy lifting for you in calculating pressure drop and velocity. They also have several line sizing tables on another tab of the excel file. I guarantee that you will learn something about line sizing if you download and examine these three wonderful resources. I know I did.


Virginia Air

Monday, December 12, 2016

Cold Weather Heat Pump Charging

Charging an air source heat pump during cold weather has always been a bit of a problem. The problem is that the amount of refrigerant circulated decreases as the outdoor temperature drops. Why is this? Well, as the outdoor temperature drops, the evaporator temperature has to drop in order to be able to absorb heat from the outdoor air. The lower evaporator temperature produces a lower evaporator pressure. The lower evaporator pressure increases the compression ratio because there is now a greater difference between the suction pressure and the discharge pressure. The higher compression ratio means that the compressor does not circulate as much refrigerant.

At a 45°F outdoor temperature,  a typical air source heat pump produces a heating capacity roughly equal to its nominal cooling capacity. At 17°F outdoor ambient, it produces about half as much heat as it does at 45°F. This difference in capacity is directly related to the amount of refrigerant being circulated. The rest of the refrigerant is just sitting somewhere – normally in either the accumulator or the charge compensator. So a system operating at 17°F outside could have perfect pressures even if it only had half of its factory charge. That is why you can be way off checking a heat pump by pressures in the heating mode.

Some manufacturers provide heating performance pressure charts, but refer to them as “check” charts. They are intended to check the system operation at specific conditions, but are NOT intended as guides for adding refrigerant. The problem is that you don’t have a good way to judge how much refrigerant is stored out somewhere in the system. I can hear a bunch of you saying that measuring superheat and/or subcooling solves that problem. While I AM a fan of checking both, they still just measure the refrigerant that is circulating.

There have been some interesting methods used, such as measuring discharge superheat. For discharge superheat, you measure the temperature and pressure of the discharge line right as it leaves the compressor. It should be somewhere around 60°F warmer than the discharge saturation temperature. So if you have a 410A system running at a discharge pressure of 318 psig (saturation temperature 100°F), the discharge line should measure 160°F. A lower temperature reading indicates an overcharge and a higher temperature reading indicates an undercharge. The surest way to charge a heat pump in the winter is to recover the refrigerant, evacuate the system, and weigh in the correct charge. If you have performed a repair on the refrigerant system, then this will save you time and insure a correct charge.

Saturday, December 3, 2016

Cranking Out The Rules

 With only weeks left in the Obama administration, federal agencies such as the Energy Efficiency and Renewable Energy Office (EERE) are finishing up work on a number of initiatives and publishing final rulings. Who are the EERE? They are a subset of the Department of Energy (DOE). These rulings have an impact on the HVACR industry. While the rulings do not have a direct effect on technicians in the field, they have a big effect on HVACR manufacturers. Indirectly they will affect us as manufacturers respond to the directives. Most of the rulings have to do with how different equipment is tested by the manufacturer, and in some cases, what equipment is covered.  Here is a list of recent rulings with links for more information.

12/02/2016 DOE Issues a Notice of Final Rule Pertaining to Test Procedures for Walk-in Coolers and Walk-in Freezers

12/01/2016 DOE Issues a Notice of Final Rule Pertaining to Test Procedures for Compressors

11/30/2016 DOE Issues a Final Rule Pertaining to Test Procedures for Central Air Conditioners and Heat Pumps

11/21/2016 DOE Issues a Comment Period Extension Pertaining to Energy Conservation Standards for Residential Furnaces

 11/15/2016 DOE Publishes a Final Determination of Compressors as Covered Equipment

11/10/2016 DOE Publishes a Final Rule Pertaining to Test Procedures for Commercial Packaged Boilers

10/07/2016 DOE Issues a Final Determination Pertaining to Energy Conservation Standards for Direct Heating Equipment  

10/04/2016 DOE Issues a Direct Final Rule Pertaining to Energy Conservation Standards for Miscellaneous Refrigeration Products

Tuesday, November 22, 2016

Check Combustion Air

With the weather getting cooler, I thought that now would be a good time to talk about combustion air. Don’t forget to check for proper combustion air. Most codes provide detailed drawings illustrating where combustion air should come from and how much you need, but there are still many furnace installations that rely entirely on air from inside the building for combustion air. In days gone by this was often considered adequate so long as the furnace was located in a large enough space. In newer homes, combustion air should always be provided.

Most 90%  furnaces today can operate using sealed combustion. In the case of a sealed combustion furnace, the combustion air is being piped in from the outside. The combustion air is piped directly into the furnace. These are easy to spot, they have two pipes: one for combustion air and one for the vent. Also, their panels have no louvers for combustion air. 

Traditional furnaces get their combustion air from the space where they are installed. Combustion air enters through louvers in their panels.Since the furnace is drawing air from the space it is in, fresh combustion air must be supplied to the room to keep the process going. Failure to supply the correct amount of combustion air can lead to negative room pressure, vent spillage, poor combustion, and CO production. All these things together can be disastrous.

When a technician checks a furnace that does not have sealed combustion, one of the first things to look for is how the furnace receives combustion air. If the furnace is in a ventilated crawlspace or attic, the ventilation for those spaces provides the combustion air. However, even these can be a problem. A large furnace in a small crawl space may not have adequate combustion air if the crawl space vents are closed. I have also seen crawlspace vents clogged with debris, effectively reducing the combustion air.  

The most troublesome installations are furnaces located inside the house in a closet. They should have a combustion air vent near the floor and another near the ceiling. Someone asked me about a furnace installed in a closet off of a bathroom. When they turn on the bathroom vent fan, they can smell gas! Another story involved a fireplace and a furnace. When the furnace came on it sucked the smoke out of the fireplace into the room. These types of stories indicate that the furnace does not have adequate combustion air. 

What if there are no obvious combustion air vents? Sometimes the vents were never provided, other times they have been covered up. I have seen combustion air vents covered with tape or plastic. Undoubtedly, someone noticed cold air coming in the vent and “fixed” the problem – thereby creating a combustion air problem. Occasionally insulation covers the grille into the attic. Another problem is using the furnace closet for storage. This is dangerous in and of itself, but it can also cause combustion air problems if boxes are stacked in front of the combustion air grilles.  For details on combustion air requirements check your local code. Unit 53 Gas Furnace Installation in Fundamentals of HVACR, 3rd ed also has detailed drawings and specifications for the most common applications.  

Saturday, November 12, 2016

Veterans Have the Right Stuff

On this Veteran’s Day I would like to suggest a way that the HVACR Industry can help those who served their country: offer them jobs. Veterans have many characteristics that make them ideal employees.

Veterans are disciplined.
Veterans have developed both self discipline and group discipline – both crucial skills for employment.

Veterans know how to work hard.
Remember, they made it through boot camp and survived years of living conditions most of us would find intolerable, all the while performing their job.

Veterans know how to be a team player.
The armed forces cannot function if everyone is freelancing. Installation is so much easier if you have a good team. Far more efficient than working alone.

Veterans can master technically difficult machinery.
Take a look at the equipment today’s armed forces work with. Much of it is incredibly complex. A veteran is someone who has been in a position where their life depended upon knowing how to operate that machinery.

Today, finding people who are good candidates for employment in the trades can be tough. Veterans already have the traits employers look for in a good employee, and that is a good base to build on. If the industry will reach out to veterans we will also help ourselves.

Here are links for people considering hiring a veteran or for veterans looking for help getting started in HVACR.

Troops to Trades 
Nexstar Legacy