As a Facilities Manager for a major commercial building, responsible for providing a pleasant environment for potentially hundreds of employees, you’re the first to feel the heat when the system fails to function properly.
Here Steve Simmonds from Spirotech, in the newly-created role of Special Projects Engineer, looks at some of the underlying reasons for problems with legacy heating systems, and suggests how they can be resolved.
I have worked in the construction sector for more than 30 years, including 20 in which I have seen how vital it is to ensure proper deaeration, dirt separation and pressurisation in a heating system for larger premises, from major office complexes to towering apartment blocks.
Over that time a number of key themes have continually arisen that have led to frustration among Facilities Managers trying to do their best with a regime they have inherited.
Sometimes these can be resolved quickly. Others require more detailed investigation. Often they go back to when the initial design was drawn up, or when mistakes were made at the installation stage. It’s not possible here to deal with individual cases, but here are my top fundamentals and what needs to be done to address them.
Firstly, there’s a knowledge gap. This happens because many mechanical services engineering courses have little, if any content on deaeration or pressurisation. So when the graduates go out into the market they are relying on advice from their superiors, but because deaeration is still relatively new in the UK they haven’t the experience to advise correctly.
It is so important with a closed system to remove the air, if you don’t you are inviting corrosion. And in taller buildings if you don’t get the pressurisation right you can affect the system dynamics and suck air back in instead of taking it out.
It is a very small part of the M & E industry but it affects the whole system. If those new to the business are being asked to specify a heating system, then getting it wrong at the initial design stage can have a big impact.
Spirotech has developed CPDs on ‘air and dirt’ and 'pressurisation', which we have extended to newly-qualified graduates so they can be better informed.
There are two British Standards that provide the relevant guidance for central heating systems. They are BS EN 12828, covering the design of water-based heating systems in buildings, and BS 7074, giving guidance on the correct specification for expansion vessels.
By adhering to both you arrive at the correct pressure range for the expansion vessel in relation to the size and demands of the building. But with some installations the designer has stopped part way through BS 7074, which means the full calculation hasn’t been done.
As a result the vessel is too small, the pressure is excessive, the membrane is stressed and you can end up blowing the safety valve. That can lead to water loss, chemical pollution, the potential for air to be pulled into the system, leading on to poor flow, water starvation and a multitude of problems simply for not doing the full calculation.
Another issue is that designers often turn to online calculators, but their accuracy is questionable and none are verified externally.
System designers must always take BS EN 12828 and BS 7074 into account, including the latest updates, and do the full calculation.
A lot of loose terminology has crept in over the years. For example, some people have the incorrect perception the pressurisation unit controls what happens in the system, and when they dial in a number they call that the ‘set pressure’ because they have ‘set’ it.
But that’s not right. Pressurisation units are reactive, not proactive. They respond to what’s happening in the system. It’s how you design the system that dictates.
Another one is ‘fill pressure’. An expansion vessel is only affecting the system when there’s water in it. Once you have correctly aligned your pre-set gas charge to the system requirements you then fill the system.
Most people fill the system to the same pressure as they set the vessel to. But this means there’s no water in the vessel because your pressures are equal and the vessel is not doing anything.
The fill pressure should always be higher than the (minimum) pressure. Most people think they are the same. That causes instabilities within the system and pressure fluctuations.
The answer here is education, possibly via CPDs, to make sure you fully understand the terminology and that it is being correctly applied.
Imperfect installation does not have to be a major error to have a big impact on performance. One common fault is the wrong size of pipe is used to connect to the expansion vessel. This affects the flow. It might not be the contractor’s fault, there just wasn’t enough detail in the drawing. Another example I came across was the pump installed on the wrong side of the pressurisation unit. Everything else was perfect. But because of the incorrect positioning, the pump was causing negative under-pressure, sucking air in at the top of the building through the air vents.
It’s not uncommon that when the contractor is called in to sort out problems like these the product manual is missing, it’s been filed for safe keeping but lost. The manual will override the system drawing and should be kept somewhere it can be easily found.
POOR MAINTENANCE REGIME
This leads me onto the maintenance regime. A contractor is called in to service the system but there is no historic data available to refer to. The manual has been ‘filed’ and the service label has not been filled in. Yes, the more modern units will provide readings via the internet but they are often in a basement so you can’t look it up on your mobile phone.
So, how can an engineer be expected to properly do their job without the correct information?
The answer to this is simply to be disciplined and ensure that good records are kept and that they are available when needed.
Everyone is under pressure to ensure value for money. But the saying ‘buy cheap, buy twice’ applies even to components for heating systems.
It can be tempting to substitute a lower-priced product than the one specified but the questions should always be asked ‘does it do the job it is designed for as well as the initial specification’ and ‘what are the lifetime costs’.
If it fails to fulfil the specified criteria, the higher energy costs and poor performance can end up costing thousands, or tens of thousands, of pounds to put right.
Cost is important but it should always be considered in line with quality and performance. A higher initial cost can mean savings in the longer term.