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The challenge of doing the job right

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By Greg Scrivener

High external static pressure caused by ductwork can cause reduced life in a refrigeration system in a roof top unit.

In this issue, I want to talk about some of the challenges associated with “doing it right.”

Every year, I teach a Fundamentals of Air Conditioning course for the Mechanical Contractors Association of Saskatchewan. We study in-depth both psychrometrics and the refrigeration cycle for two days and then bring it together with a residential air conditioning focus in a practical lab where we work on two different air conditioning systems—one with a TX valve and one with an orifice metering device.

When I first started teaching the course several years ago, I misjudged how much time and effort would be involved in covering what I thought were simple concepts such as superheat and subcooling. I frequently forgot that this stuff is not baked into everyone’s brains automatically and I often struggled to move at an appropriate pace when I was trying to explain something; I’m fairly certain the junior engineers I work with would probably say I still do this. (This is sometimes called the curse of knowledge bias.) I am surprised that someone could install air conditioners for years and not really understand what was happening in the pipes.

Autopilot

Manufacturers have done a really good job at making our life easy. Most of the time, when you open the service valves to start up a residential air conditioner, it just works. Obviously, this is good because it makes the installation easy, but it has some downsides. It means that you can install hundreds of air conditioners and never really have to understand how they work. You don’t really need to understand superheat or subcooling or how the compressor operates at low load. Everything works just fine—until it doesn’t. And as long as “it doesn’t” happen after the warranty period, then everything is good. I have worked on residential air conditioners that were on their third condensing unit in 10 years with no warranty provided. If a soap box was near, this is usually where I would get on it and proclaim the virtues of having adequate knowledge and proper installations and start-ups; I’ve been on that soap box many times before.

Personal project

This summer I decided to install air conditioning in my house. This will be the third house we have lived in where I have personally installed the air conditioner and up until now it has always been a curse. In the previous two cases, the rest of the summer ended up being so cold we didn’t need air conditioning at all. This summer, we lucked out and I got the air conditioner installed just before a 30C plus week. We live in an area with no access to natural gas, so I considered putting in a heat pump to save some propane during the shoulder seasons (a few years ago, wholesale propane where I live went above $1 per litre in the middle of winter). On top of that, we were thinking about putting in a small pool and a heat pump would be able to work its magic and cool the house at the same time it was heating the pool. I ended up ordering a 2.5-ton heat pump.

Do your measurements

The exercise of figuring out what heat pump to order and how to design it to do all the things I wanted—cool the house; cool the house and heat the pool; heat the pool only; heat the house—will likely end up in a future article. It is much more complicated than it seems at first pass.

For this summer, I just put in the heat pump. I installed the piping, did a pressure test and evacuation, opened up the line set and turned on the power. Guess what? It worked.

According to the installation manual, I needed to put in a few ounces of refrigerant, but everything seemed great. Nice high suction pressure and exactly what you would expect for a condensing pressure. I didn’t add refrigerant, I didn’t check the superheat setting of the TX valve, and I didn’t measure the subcooling. I flipped the thermostat to heat and that worked too. It has been running for a month in both heating and cooling and I haven’t touched it again. I am that guy.

The author’s heat pump—installed and turned on.

Lifespan of a system

I’m sure that a lot of other industries are similar in this regard, but one of the challenges we face in the refrigeration and air conditioning industry is that we can get away with a lot. Many of the errors we make installing or servicing a system have significant long-term effects on both lifespan and energy use, but don’t dramatically affect the day-to-day operation. We’ve discussed before about the cost of using too small of a suction line or not installing piping with good oil return. We’ve also discussed about not properly cleaning condensers and adjusting/ verifying superheats. A system with a high superheat and dirty condenser has a slow death sentence imposed on the compressor because it will operate much hotter.

Residential air conditioning is particularly challenging because in most of Canada’s climate regions the systems don’t actually run very many hours per year, which means that problems can take a really long time to show up. Commercial systems run more, but still not that much. With commercial refrigeration systems that have to operate all year, you start to see the consequences of poor installation and maintenance practices more quickly. This does not mean the refrigeration mechanics servicing commercial equipment don’t have the same challenges. Commercial systems can be much more complicated than residential air conditioners and the technicians that service them have to know a lot more, but I suspect there is just as much “flick the switch and leave.”

Resist taking shortcuts

All of this presents a problem for our industry because we can get away with it, it can appear less expensive to do exactly that. For example, if it takes two hours longer to do everything properly and verify proper operation on a residential air conditioner installation, you could save 100 hours by taking shortcuts while installing 50 air conditioners. That means, from a cost perspective, if only one of those 50 goes wrong enough to take a few extra days to get working right, or maybe requires a warranty replacement, you can still end up ahead.

So, what’s the problem? The problem is that this attitude decreases the requirement for knowledge, and it discourages investment in education for technicians. Without well-trained and educated technicians, it becomes more and more challenging to solve the hard cases and we become an industry, who in large part, doesn’t have adequate ability to fix what has been installed at a reasonable cost. I don’t believe this is a healthy place to be and I strongly encourage you to do what you can to encourage training in your organization. For me, that means I better go start-up that heat pump properly.

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