Boiler energy saving is like running a bar ?

At kWIQly we noticed huge amounts of energy can be saved by controlling boilers or furnaces better. Unfortunately independent reliable advice is hard to find. 

Naturally there are vast numbers of companies trying to sell this or that "solution" , but can they be trusted?  

What I hope to do here is simply to provide a primer or 101 on the subject. If you know what you need - you are more likely to buy it, and not what the salesman is selling. So how do we (you - but let me talk on this occasion as if I'm on your team) save energy?

It's worth looking at this through the eyes of a poor college student (put yourself in his position) who is buying a round of drinks in a crowded bar,  three rules must be observed, not in any particular order.
  • You find out what is wanted - right now (not on the next trip to the bar - not your problem)
  • You try to deliver drinks with least spillage (maximise bang for bucks).
  • You refuse to pay for what the barman spills
Meanwhile the bartender pours what you need (wasting as little as possible) before handing it over. If in some odd world there where more bartenders than were clients and they got ahead of themselves by pouring too many the rest is their problem.

Back in the real world of energy management things are very similar, but there are also some very important differences. Assume we have three boilers (bar-tenders), that you will really deliver heat via pipes (instead of wading through a sea of drunk students) and most of the year you more than enough boiler power (three bar tenders is more than plenty in an empty pub).

The important differences are as follows:
  • Spillage is absolutely unavoidable - the rate of heat lost on the way back from the bar is directly proportional to how full the drinks are ie the thickness of the insulation Maybe we can imagine a little railway track that delivers beers like luggage on a carousel at the airport or dishes in a sushi bar. The hotter the pipe (the fuller the glass)  the more is lost. We could reduce this "transmission loss" through improved insulation, which has very predictable effects (but the benefit is lower the less you are wasting - so it makes sense to evaluate waste before investing).
  • Bar tenders are lazy, boilers are not! A bar tender will only pour a beer when necessary but a boiler lives to work. A boiler can be turned off or turned down, but given the freedom to act within the limits of its' own thermostats a boiler will spend your money just as fast as it can (think of serving water at the bottom of Niagara ) it would spill less if you could turn it down between servings !
  • Boilers are more efficient the harder they work but busy bar tenders make mistakes. So if you are going to let a boiler run, you do want it to run as hard as possible.
  • People know how much they want to drink very accurately (I did not claim this is good for them) - generally it is a simple question of more or not more. Buildings are more choosy -they want a little or a lot or just enough heat to stay comfy.
  • Final difference, heat can be wasted if delivered after people have left the building, but once a bar clears, the drinking stops.  Would you sack a bar tender who left a beer tap running overnight ? - Me too !

So with these differences comes a set of problems, which is not as instinctive as buying a round of drinks.  However, (and perhaps surprisingly) the optimum strategy is not all that difficult to figure out.  Lets go ...

We need to apply a simple set of rules about when to work and when not !
  1. Always deliver heat at as low a temperature as you can, to get the job done (carry half empty beer glasses to avoid spillage unless a full glass is ordered).
  2. Use the least number of boilers possible to get the job done (bar tenders are more clumsy when overworked) - boilers are more efficient when working really hard.
  3. Do not let a boiler "idle" or "tick-over", if it is OK to switch it off -  do so  ! (the hard work reason).
  4. Rooms don't know how much heat they need or when they need it - like drunks.  Watch what is needed, when it is needed and deliver as rarely as possible (off at night)
There is some devil in the detail - lets get our mops out and see if we can sort out that spillage !

How fast should you pump the water round the system ?

Boilers get hot and give off heat - also heat goes straight up the flue (chimney) if it can. Ideally when a boiler is burning gas, you want to carry away as much heat as possible, otherwise it gets lost (rather like a barmen stacking hundreds of beers on a bar that nobody is delivering).  The implication is that heat should be carried away fast.  Each boiler has a "rated flow rate", if you burn fuel without making sure water is pumped fast enough, you are pushing energy up the flue.

You can save electricity by using a variable speed pump  ( a VSD drive or frequency inverter matches the AC supply to a lower rotation speed ) BUT, if water is flowing through the boilers slowly you can lose much much more (a pump may use a few kilowatts to satisfy a boiler that delivers megawatts.

The heat should be circulated around the building fast as well, if it is delivered slow, it must be delivered hot (more losses at boiler and along the journey = full glasses).

If the point of delivery throttles flow when satisfied (the drinkers ease up on their pace is analogous to air conditioning unit cooling or heating valves closing), then there is an opportunity to deliver less - so reduce the boiler heat (deliver emptier glasses) to keep the rate of pumped delivery high - a VSD drive can be an excellent tool in the armoury for this

How many boilers ?

Too many bar-keeps is a really bad idea (hot metal)  suppose you need to deliver a number kW load and you have two boilers that can deliver 650 kW and one that can deliver  400 kW ( use 1000BTU instead of kW if you prefer - the analogy holds) - Its all about how hard you want to push

This means
0 - keep all boiler off 
1-400 use the 400 kW boiler
400 - 650  use the 650 kW boiler
650 - 1050  use the 400 kW boiler and the first 650 kW boiler
1050 - 1300 use the two 650 kW boilers
and above this use all three boilers.

This is called demand sequencing and from three boilers you can have six steps. For historical reasons (a reversible camshaft) there are traditionally only two sequences of 4 possible steps implemented summer-winter-winter and winter-winter-summer (where the bigger boilers are called the winter boilers) - This is very weak thinking.  What is notable in the "correct" solution is that the smallest boiler goes on and off at each load step change.  This is very important because a "blown" or "charged" boiler wastes a lot of energy switching on or off (the combustion chamber is purged with cold air before and after burning to reduce explosion danger -by clearing out un burnt gasses.

Demand management - How do you know how much to pour ?

Sorry - this is too big a topic- the subject of a later post, but as a starter, given that buildings are built to keep heat out, and that we sleep at night it should be no surprise that weather and time of day are the two biggest single factors in deciding.

Hope you enjoyed the post - follow @kWIQly to be advised of the future instalments

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