Heat Pumps.

Interesting article, thanks. I guess we all have our anecdotes about heating systems and we have just replaced our gas boiler with another so I have been paying attention to any recent developments. I am curious as to why your average plumber can't fit heat pumps though. The "accreditation" required surely cannot be more onerous than they already need to fit a gas boiler. The lad who did ours has to be plumber (obvious), gas safe (so that covers chemistry), basic electric qualifications/skills. All this he took as standard for a plumber. The only things extra I can think of are the "green" credentials to be able to big up the benefits. He was already well aware of heat pumps and their downsides - in our case ripping out all the pipes and rads which will rarely be cost effective. New builds are a different matter, and they do fit them along with AC units in many cases. (p.s. he did a great job.)

Yes, interesting, and not at all surprising.

I have gas heating (an efficient boiler), use approx. 40K-50K kWh per year, depending largely on the weather. I just got a quote to add an air-source heat pump. That involves also changing the accumulator (called the "hot water reserve tank" in the diagram). Detailed estimate: €44K. The air-source heat pump itself will cost nearly €19K including installation; the accumulator just over €13K including installation. This is rather different from the "ten grand" mentioned in the article.

Concerning the qualifications of the installer, a colleague had a heat pump installed in a house he renovated to high-efficiency standards. It took the family a year to get it working properly. The experience base is not there yet.

Here is a tale about the importance of experience.

We have had problems for years with the heating shutting itself down multiple times a day, during "warmer" weather (i.e. outside temperatures above freezing). It has been annoying, but during Covid not particularly difficult since I am at home all the time and can easily pop into the basement to reset. During consultations on my heating system modifications, two different contractors looked at my installation and said "these pipes [the boiler connections] are too small". One of them just suggested "replace"; the other suggested, rather than routing the boiler output directly into the heating circuit, instead routing the output into the accumulator and having the accumulator supply the heating circuit. 

In fact, what it was is that the target water temperature is set by (inside temperature) + (Factor x (insideT - outsideT)). And "Factor" was chosen in the regulator to be too high. The maintenance technician called the boiler company rep from the basement, who had him run through a variety of checks, and they hit on that as the likely problem. Looks like it - the heating has run problem-free since then. The point is that not even the maintenance tech, who deals with these systems day in day out, knew or thought about that. But the company rep did, presumably because he has a much wider overview. The maintenance tech was unable to explain to me exactly what it was about, but he mentioned "slope", the company's name for the parameter, and I went into the company documentation for the controller to find out what was called "slope" and hit on it.

The math and physics behind all of this is trivial, to someone like me. Also, I know about the design of control systems. But wading through documentation to find exactly what the tech was on about, and interpreting it back into my preferred conceptualisation took me hours. I didn't get to false "slope" as a possible causal factor, though in retrospect, knowing the parameters of the control law, it is now obvious.