Knowledge Sharing: Point of no pressure change

I am going to put together some knowledge sharing of points I feel are never really taught much or discussed, leaving many installers unsure of what to do, but feel silly sometimes to ask, but in my opinion there is no such thing as a stupid question, but not asking and doing something wrong is stupid.

The point of no pressure change in a heating system is the point where the expansion vessel is connected, basically at this point the pump cannot change the pressure to create circulation, this is similar to the neutral point on an open vented system and in reality we should be following the same principle as we used to with the neutral point on open vented systems, with the neutral point on an open vented system the open vent and cold feed were always on the suction side of the pump, so the pump was always pumping away from the neutral point, this is the same for a sealed system and the point of no pressure change, you need to always pump away from the point of no pressure change (Expansion vessel connection)

Now before I get more into this, I would like to emphasis this information is out there for all to see, this is not something I have invented myself, there is a great book out there written by Dan Holohan called "Pumping Away" where I gained my knowledge on this information.

Now within a sealed heating system, for the pump to create circulation the pump will create pressure  differential rather than pressure, now at the point of the expansion vessel connection to the system because the pump can't add water to, or remove water from the expansion vessel the pump cannot change the pressure within the expansion vessel, this is why its called the point of no pressure change, the circulator will respond to the expansion vessels location, raising or lowering the differential pressure based on that location, if you pump away from the expansion vessel, the circulator will add its differential pressure to the systems static fill pressure, if however if you pump towards the expansion vessel the circulator will remove its differential pressure from the system static fill pressure, and if the pump's differential pressure exceeds the system's static fill pressure, the pressure at the pump's suction will be below atmospheric and air will enter the system, you then have problems with the system.

Here is a diagram from Caleffi that may assist in understanding this principle, unfortunately its in psi, as its from USA, as I could not find anything in metric covering this information, why is that?

If you are interested in reading further the Book, "Pumping Away" is available HERE 

I hope this proves useful to some, if you have any questions please ask away and let me know if there is any subjects you would like me to cover

Frozen Condense Pipes

So, we have just had an extremely harsh cold spell, temperatures as low as -10 in places on occasion, last time we so temperatures like this for any sustained period, was about 5 years ago, I remember well we had exactly the same problem back then as we have experienced this time, FROZEN CONDENSE PIPES.

Now what should we as an industry do about this, I ran a poll on Twitter, yeah, I understand that its hardly a major poll, but just wanted to gauge opinion from installers, I gave the choices, do we need regulation change to either

1.Not allow condense pipes to be run externally
2, Require insulation and trace heating on any exposed condense pipe

I also added a third choice

3. Do we just except that we may get sub zero temperatures say every 5 years and just except external condense pipes may freeze.

So far with one more day to run of the poll out of 92 installers who voted so far 47% the largest proportion went for No3 excepting the occasional freeze, now I sort of understand this response, the UK mostly fuelled by the media, do tend to over hype everything and we take weather like this as an armageddon, it is rare for us to hit these sort of temperatures in the UK, as stated earlier its 5 years since I remember such low temperatures, well this is for most the UK, I understand Scotland is often far colder than we experience further South, however, I don't agree with the poll result.

We only need heat in the winter and we certainly need heat when we hit temperatures of -9 but for boilers to fail in times when they are most needed due to something that is preventable is not really acceptable in 2018, now I don't do reactive work, so I did not go out defrosting frozen condense pipes and I take my hat off to all those who did get out in treacherous conditions to help people with such problems and I hope you earned well, you have to reap the benefits when times are good, now I have seen some external condense pipes via Twitter which when run externally have been done to what we consider correct methods, short as possible runs, mostly vertical and in 40mm pipe and they still froze.

I personally think there are 2 problems here, lazy installers who just want the easiest job possible so take the quickest way with the condense, rather than looking for alternative possibilities that could keep the condense within the thermal envelope of the building and second, customers not willing to pay for alternatives that may cost a bit more to the install, but would save them losing heat in such cold weather, but what do we do about it.

Now I know at the start I mentioned regulation change to enforce things, but in reality I am against such things, I am not one for big Government telling us what to do, this is something we as an industry need to address ourselves, we need manufacturers and trade bodies to publish good practice methods, stating that condense pipes should NOT be run externally, training bodies, need to drum it in to the new and upcoming people within our industry that it is not acceptable to run condense pipes externally, again we need the industry as a whole, manufacturers, trade bodies to educate the public via newspapers, and online that installers will always try and keep their condense within the thermal envelope to prevent freezing and that this will cost them more, but is worth it rather than been without heat and paying an emergency plumber when it does freeze, so they will pay in the end, but it needs to be done while the iron is hot, like NOW, when it it fresh in peoples mind how horrible it was to be without heat, because come spring, it will all be forgotten.

Another point that some have raised on Social Media is the type of boilers that have the issue with freezing condense tend mostly to be those that just trickle the condense constantly, and not so much those that release a larger slug of condense in one go, maybe this is another solution for manufacturers to consider

So what do all you installers think, this is our industry so lets talk about issues within our industry

Thank You for Reading