BEM 4000

[BEERMONSTER]

I work for a charity and we are currently looking to improve the efficiency of our Ideal Concord CX240 boiler to redice our LPG bills down from around £10k.

At present, there is a Danfoss BEM 4000 unit installed, but over the years, the stats have become damaged and not replaced. As such, the BEM unit has been bypassed and is only used to turn the boiler on/off when there is a demand for heat. I also understand that the boiler is running on its internal stat which is inefficient and causes expensive dry cycling of the boiler??

We have been advised that the BEM unit uses a very crude method of controlling the boiler and applying its weather compensation, and we would be better fitting a more modern boiler management system to just control the burners and stop any dry cycling. One such example of this is is a vector boiler management system.

http://www.vectorgroupuk.com/solutions.html

To reinstate the BEM unit would only cost £51 but it is unclear on how effective this would be at saving money when compared to the Vector unit which doesn't have the weather compensation and costs £1600.

For some back ground info the heating is split into 3 zones with a 4th zone for HW. Each zone is controlled by its own time clcock and also has 30/60/90 min boost switches to allow our guests to call for heat outside the normal time slots. Each of the time clocks/boost switches send a signal to the BEM 4000 for heat and also opens the require motorised zone valves. Each radiator is fitted with TRV's and there are no room stats.

I am keen to get some opions on how best to proceed with this as all we seem to be getting is companies pushing their own devices and not what is in our best interest.

Is it best to stick with the BEM 4000 or replace it with a more modern device?

How efficient is the BEM 4000 going to be when compared to more modern devices?

How good is the BEM 4000 at stopping the Dry Cycling??

Does anyone have any recomendations on possible replacement which would fit into our current setup easily?

Does the weather compensation side of things really work?

Thanks in advance for your responses

Andy

 

[doitall]

Could the Concord CX240 be converted to LPG. ???

Before you chuck £1600 quid on some gadget, I would suggest you get shot of the 80Kw Monster boiler for something a little more modern.

If you are serious about making savings, TRV's, room stats and a proper controller would slash the bill for a start, then perhaps you should look at open therm etc, and educating the staff.

Without a doubt though the first thing is a new boiler.

 

[Agile]

As fas as I understand it the boiler is already running on LPG which is much more expensive.

For that style of boiler I dont see it as that inefficient.

However, the project needs to be properly managed. Spending £1600 is not the way to save money.

Your description shows up a glaring inefficiency!

There are no room stats so the boiler stays on even when all rads have been turned off on their TRVs.

Simply adding three room stats will probably save 15-20% of the gas bill for an outlay of about £100 with a sympathetic engineer.

If I lived near there then I would concoct a weather compensation system BUT being a non condensing boiler that will not greatly improve efficiency. WC relies on making a condensing boiler spend more time condensing and can increase efficiency by up to 12% but 4-6% is probably a more typical improvement in efficiency.

Even without WC, manually applied WC can be made by adjusting the boiler flow temp according to the weather!

Also timing the HW to be on at the same time as the heating will save a little too.

For £100 I would expect that I could save you about 20% of the gas bill if I lived close by.

Tony

 

[BEERMONSTER]

Given the nature and size of the building, we need a monster boiler just to heat it. (exposed location in the middle of the yorkshire dales and solid stone walls don't help things)

As a charity, we don't have loads of money to throw at installing a new boiler. I have spoken to ideal and they have advised the boilers equal in todays market is a Concord CXA and this is only 2-3% more efficient than the current boiler. Moving to a HE boiler would save us more, but then the cost of buying the boiler/controls, converting it to LPG and getting it installed go through the roof which is something we cannot afford at the moment. We are planning to change the boiler when funds permit, but until then we are looking for a quick fix to reduce the amount of LPG we are going through each year. What we save now can go towards a new boiler.

Just out of interest, what boiler would you reccomend as a replacement? I thought the cx240 was about 90kw and 250 000 btu, and we have 44 radiators and a massive HW tank which feeds 8 showers.

As mentioned, we have TRV valves on the radiators and the building is split into three heating zones. We have tried using room stats before, but found they didn't play well in our building as you would always end up with rooms that were too warm and some too cold. Moving to trv valves sorted this problem.

With regards to the controls, this is where the headache starts. The trustees/staff live 60 miles away from the building and we rent the place out to various groups like schools, scounts and famililies wishing to take part in recreational/educational activities in the yorkshire dales. The trustees do get up to the building as often as we would like, so we had to install some fool proof controls to stop clients leaving the heating on 24x7. So we have time clocks locked away in the plant room and boost call switches in the main building for clients to use. I beleive the open therm controls you suggest are for modulating boilers which i'm sure ours isn't. Hence why a burner controlling device like the BEM 4000 or the Vector unit would possibly save us money.

 

[mickyg]

wouldnt be surprised if your overpaying for the lpg in the first place. A phone call will be your biggest saving. Shouldnt be paying anymore than 45p/litre. Currently getting my customers a 2yr fix as well at 45p.
As above, the boiler is inefficient, and an expensive controller won't bring massive savings.

 

[doitall]

I'll try that again just for Tony.

The Concord CX range were suitable for natural gas only, and I wasn't aware they could be converted.

Don't know so thought I'd ask.

 

[Agile]

I explained how you could save perhaps up to 20% on the gas bill.

Unfortunately you dont seem to have read it or tried to understand it.

With a very small expense you could save a lot.

Replacing the boiler is expensive and will give very little saving at all.

If I was given the job then I would use two condensing boilers of the domestic style as their price is competitive. With the right controls that would save perhaps up to 22% or more. But as I explained above, you could save most of that for just £100.

Tony

 

[doitall]

A Rinnai instantaneous water heater for the showers etc would save a load of dosh against heating a massive cylinder from and equally massive boiler.

 

[BEERMONSTER]

Thanks for the replies guys. Tony, I hadn't seen your response as I was busy typing myself.

I understand what you are saying about the room stats and can see your theroy behind it. However, when we moved away from coal to LPG and installed the boiler almost 20 years ago, we originally had several room stats and found parts of the building were getting too warm, some not warm enough and some were just right. This led to quite a few complaints and we eventually moved to TRV's instead. But as you say, the down side to this is the boiler will not switch off when the building is up to temperature!

To try and get around this, we have set the time clocks to just keep the boiler on long enough to bring the building up to temperature (2hours in the morning and 2 hours in the evening). If the clients want more heat, they have to press the boost button to give 30/60/90 mins extra heat. Probably not the most effective way, but better than leaving the boiler on for a few extra hours.

Given we have tried room stats and failed with them in the past, would you still look at fitting these again???

 

[BEERMONSTER]

Just giving what has been said a little more thought, there would appear to be two areas of possible improvement in our setup.

Better control over the demand for heat - ie fitting room stats to turn the boiler off when the building is up to temperature.

Better control over the way the boiler fires - I understand the internal thermostats on these types of commercial boiler are not very good and waste a lot of energy due to them firing when not needed. This where the units like the Vector BMS and BEM 4000 come into play.

I understand both of these will save money, and addressing both will save even more.

I will certainly look at the rooms stats again to see if we can overcome the problems we had in the past. I was also looking at the room stats and TRV's which can be set at a fixed temperature, this would stop people playing around with them once we have got everything setup correctly.

As for the boiler control, is something like the Vector going to give better savings over the BEM 4000 to justify the extra expense. They do offer a free trial to show what savings can be acheived before you are invoiced. This is done by two meters on the unit which show the burner demand time and the actual burner firing time.

As we are on LPG, we don't have any way of measuring how much gas we are using in a set period, just how much has delivered. Given this, I like the meter feature on the vector unit as it will give us a more accurate idea on how much we would be saving. Also is we fitted this device first and recorded the demand time for 1-2 months and then fitted room stats, we would be able to see how much we are actually reducing the demnad by and how much we are saving.

Forgot to mention, we have a very keen when it comes to the cost of LPG, and currently are paying 41p per llitre, so at and average of 45p its a good deal.

 

[doitall]

looks like I'm ignored again. Bit a luck I'm off on holiday in the morning

 

[BEERMONSTER]

Sorry doitall, I have read your response, but not replied to it.

The building is not supplied by mains water.

Our main supply is from a bore hole which gives approx 45 psi, which I uncertain if this would be enough to run 8 showers at the same time.

Our second backup supply is low pressure natural spring water supply.

At present all the taps and showers (except kitchens) are gravity fed from a number of storage tanks in the attic, so unable to use instant water heaters.

Is the water heater you suggested able to run off LPG and be sufficient to supply 8 showers?

To be honest, I think most of our energy is used in heating the building rather than hot water, but it is something to consider when we eventually look at upgrading the boiler.

 

[doitall]

You may be surprised how much it costs to heat the water, especially when the heatings off.

I reckon a small boiler just doing the water water would pay for itself inside a year or two.

 

[BEERMONSTER]

I've just been discussing this with another trustee, and had a bit of an idea.

Remove the current boiler and replace it with 3 HE domestic combi boilers with WC. 1 for each of the existing heating zones.

For the hot water, connect all three together to supply the hot water on demand. Would there be enough flow rate for 8 showers on 3 boilers?

Also while fitting new boilers, look at say open therm controllers and room stats at the same time to modulate the boilers correctly according to demand.

Is it possible to do this?

On the back of this idea, what would be the best workaround should a boiler fail? Valve system to merge 2 zones together to run off one boiler or say a 4th boiler on standby?

Can most domestic boilers be converted to run on LPG?

Just another possible avenue to price up and explore.

 

[doitall]

Don't know who we have in your area to look at the job and give best advice with a price.

I would look at 3 maybe 4 condensing boilers all connected as a cascade, (do a google) and you'll get loads of info.

The hot water is a big expense on such a big boiler and should be looked at separately.

Off the cuff if the trustees were willing to spend £10k give or take a k or two for the right plant and controls, I think you could knock 30-50% off the gas bill.

Problem is it needs to be surveyed and the best plan on paper, there's a couple of good guys on here that could do it but maybe too far south.

Untitled

• doitall
• 28 May 2012
• 2