Hi all,
My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? I'm not quite sure how they work. What are their advantages over standard pumps?
Francis
Yes I do.
Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases.
I found that mine therefore runs a lot quieter than erstwhile models.
There are a few other features such as a deblocking function.
.andy
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WOOOOOOOOOO HOOOOOOOOOOOOOOOOOOOOOOOOOOOO
Thanks Andy. That installation team can install my pump right away!
Francis
I assume you are woo-hooing re: the 4 birds in cat suits. Those birds go to trendy bars and pull out their Alphas while ordering a Martini.
Yes - quite simply the Alpha pump is the biggest advance in plumbing in years and should be mandated to be put into every home thereby allowing us to close umpteen power stations.
Okay bit over the top but once you've tried one you won't want to go back to anything else.
Or better still, pump your install!
With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature.
Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion.
People use these having TVRs on all rads. Boilers require a minimum flow through the rads, using TRVs on all will reduce this flow. A flow switch that cuts out the burner is required when the flow gets below the boiler makers stated flow.
Using a by-pass on a "modern" condensing boiler defeats much of its purpose. Older condensing boilers had the same design specs as regular boilers: the Ideal Minimiser stated 80C flow and 11C delta T on flow and return. The makers did say that you can stretch it to 15C.
Not exactly.
Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head.
Only close to the point of total closure.
it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway.
.andy
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Hi Malcom,
Great site. I have not heard BESPOKE since that TV show "Never mind the quality, feel the width". I'll have a look in detail later.
We have a back boiler unit at the moment, which is coming to the end of its life.
I have an automatic by-pass valve in the circuit, but I'm not sure how to set it. Any guidance on this appreciated.
Francis
Would it work as well on a microbore system ?
My installation consists of 22mm (may be 28) pipe which does a circuit under the 1st floor. From this, each rad has a tee down to microbore (probably 10mm). Only a short distance for the upstairs rads and down behind the plasterboard walls for the downstairs rads.
I guess there is more resistance in this setup than an 'ordinary' setup.
Alan
The thing that worries me about this discussion, though, is that if the Alpha has reduced its power/speed/head because the flow has reduced, there may not be enough head to open the by-pass. There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen?
By setting the bypass appropriately.
You can also adjust the pump.
.andy
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It will work just as well on Microbore.
My installation, heating loop, conists of a two-floor teeoff with, on each floor, the distribution pipes stepping down to each rad. Every rad is fed by 10mm pipes but the distribution pipe steps down at each stage; -
| | | Rad Rad Rad | | | I guess there is more resistance in this setup than an 'ordinary'
Generally the pressure drop across a microbore system is a bit more than on 15mm systems but not hugely so if the system was designed properly.
Tube resistance is higher, but as long as the flow carrying capacity was taken into account, it should be OK. You can do a sanity check on this if you go to the Copper Development Association website. There is a downloadable paper on pipe sizing for domestic systems. If you know the lengths of pipes reasonably you can calculate the maximum flow rate and heat transfer possible. The basis is no more than 1.5m/sec to avoid noise from the pipework. Since flow rate and heat transfer are linearly related you can determine the heat transfer allowable.
Rule of thumb, this equates to about 1500W over typical house distances of a few metres for 8mm and 2500W for 10mm.
You can then check your radiators. Measure them and look at the number of panels and fins. Then look at a/the manufacturer's web site at the datasheet and you can get the nominal power output. If you have a conventional non condensing boiler, multiply the radiator manufacturer number by 0.9 to get the true output. You only need to do this for the largest radiators.
As long as you are reasonably close to being within the limits, then all should be well.
Some installers through laziness or incompetence or just hoping, may have overloaded the pipes. This may not be a problem. All that will happen is that you may hear noise from that part of the system or the radiator runs below capacity.
I have an 8mm system, and when it had an Alpha pump on it, it worked well. Some of the radiators were 20% over the nominal limit for the pipework. I should add that the reason for moving it was because I now have a boiler with integrated pump and that is controlled linearly by the boiler controller according to heat load, so nothing upon which the Alpha could improve. The Alpha is still doing good service in a separate circuit for my workshop
.andy
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Andy,
I'm now puzzled.
Is it a choice between
Standard pump AND automativ by-pass
against
Alpha Pump AND no by-pass
Francis
Not as far as I am concerned.
You can use an Alpha pump either way.
The point comes back to the earlier one of what do you want the boiler to do when the flow becomes low as the result of the TRVs beginning to close.
If it;s a conventional boiler, you want it to be locked off by the room thermostat when the flow becomes so low that the boiler begins to short cycle as a result of the high boiler output vs. low demand.. That will happen if if the flow rate is low because the TRVs have reduced it or if the return temperature is high because there is a substantial amount of bypass. Therefore you have the room thermostat in a room without TRV to put that additional control in place and stop the boiler shortly after the TRVs have reduced the load.
With a condensing boiler, you still want to detect this case, but because the boiler will have modulated down adjustment will be easier.
It's useful to have a bypass anyway, to cover the case where the boiler has been in full burn and the heat demand is suddenly satisfied
- this is the pump over-run case. Some boilers have very low water content and if they have an integral pump can live with an internal bypass as well. If you have an external pump, then an external bypass is normally used anyway - in the form of a lockshield valve across flow and return. Using an automatic bypass instead is a better idea just for that since you are not shunting the flow back to the return until either the CH has reached low demand or turned off altogether.
.andy
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Well, I'll read all that later. I have to go and paint a door now.
I'm leaning towards the alpha and it's installation team!
Which one is you and wich one is Ed?! ;-)
Francis
The one I have just says set it 20% above the on state head so what I'd do is first balance the system with all TRVs open and bypass set to off. Then reduce bypass until there was some flow (pipe gets hot) then turn bypass up a bit so there was no flow.
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