Heat bank & boiler connections

[Dan Robinson]

Well my condenser sits quite happily with a delta between 21 and 35 degrees. I can run it in a variety of ways, with the store cooler than 80 should I wish. The PHE is rated at around the 100kW mark, so I cold quite easily get a respectable performance with a store temperature in the Mid 70's....In fact here is part of the spec sheet for it:

side 1 side 2
Inlet temperature : 75 °C 5 °C
Outlet temperature : 30 °C 50 °C
:
Flow rate : 1.938 m³/h 0.5317 kg/s

Plate heat exchanger
Heat load : 100.0 kW
Total heat transfer area : 0.836 m²
Log mean temp.difference : 25 K
Calculated pressure drop : 13.6 kPa 12.7 kPa
Number of channels : 19 20
Number of plates : 40
Overall HTC : 5100/4780 W/m²,°C
Oversurface : 6.7 %

I am not lecturing you on energy efficiency. Merely that TS are perfect for a condenser.

My store came with dual stats which I can set to ensure a return temperature below dew point and minimise short burns. Currently though I have a sensor communicating between boiler and store which has similar buffering characteristics but allows closer monitoring of the boilers various sensor curves through software.

I can assure you it condenses rather a lot.

The radiator circuit can come off at various points in the water column giving some control over flow temperature, but frankly with a modulating pump, full TRV coverage (except where the room stat is) and heavily lagged pipes, WC is not the be all and end all as the boiler's burn is regulated by the store.

Oh, and on mine, the only blending valve is the TMV valve coming off the plate - 'cos I don't want water hitting the taps at 70 degrees


I accept I should have said boiler efficiency rather than cylinder efficiencies, but if you want to heat a cylinder up quickly and to 63 degrees, then no steamer is going to condense anywhere near as long as a steamer on a properly set up TS.


I won't lecture you if you won't lecture me eh?


*edit* my store is set as hot as it likes until the bottom third hits around 55. This is sensed by the boiler's dedicated cs. The flow temperature is limited by the boiler PCB to 84 IIRC.

 

[Onetap]

What you wrote counters what the makers say..............

Well, fancy that!

 

[DeltaT2]

As with the other thread, the practical people that work at the coal face know how poor these types of units are. There's so many disadvantages to fitting them that will cause many customers money, in running costs & ulimately, they fail. A poorly designed product, so much so that you'll never come across one in any other country.

 

[Dan Robinson]

Well, as I have mentioned before, I have one, and have tried several methods of controlling the temperatures and monitoring stratification.

The thing is plastered with temperature gauges, and sensor pockets.

I have also had thing bad boy set up on it monitoring heat up, cool down cycles along with boiler F&R temps.

I can assure you I am not an armchair googler.

 

[Onetap]

Well my condenser sits quite happily with a delta between 21 and 35 degrees.

I am not lecturing you on energy efficiency. Merely that TS are perfect for a condenser.

You didn't address any of the points in my earlier post.

Having the boiler & heating system flow to 80 degC when most heating systems require 70degC or less under design conditions (-3 degC or so) and will operate at much less for most of the heating system, is inefficient and daft.

The Vaillant Ecotec has a modulating burner and electronic controls to enable it to adjust its heat output to give the optimum flow temperature.
Hooking an Ecotec up to a heat bank makes as much sense as a turbo-fan engine on a hay wain.

Most of your argument is based on the production of DHW which is usually a small anual energy consumption compared with space heating.

Heating the DHW to 75 degC+ and then using a TMV to mix it to the recommended 60degC is inefficient and daft.

A poorly designed product, so much so that you'll never come across one in any other country.

They are used, where there is a need to store heat from a non-condensing heat source; usually a heat store insulated cylinder.

 

[Dan Robinson]

But I did...

The radiator circuit can come off at various points in the water column giving some control over flow temperature

.

Where I have mine is positioned, this equates to around 70 IIRC;

I am not heating DHW to 75. I am heating a store up to xx ° . I play around with it to gauge performance vs. energy use.

It just so happens in its current configuration, my boiler thinks it is heating a DHW cylinder so does not modulate, but shuts down when its return temp is at the cylinder set point. This is below the dew point.

I wouldn't fit a Vaillant again if you paid me. So frankly don't care that it can modulate. However, if a boiler is condensing with a huge delta, why worry about modulating? Modulation is for matching heat load. If the heat loads is such that modulating is not required then who cares? the boiler is condensing the whole time.

In my case the actual top temperatures are adjustable. As are the shut off temperatures.

Now, how about a hyrbid system..... an unvented cylinder reheated through a plate rather than a coil.... neat idea huh?

 

[Onetap]

....In fact here is part of the spec sheet for it:

side 1 side 2
Inlet temperature : 75 °C 5 °C
Outlet temperature : 30 °C 50 °C
:
Flow rate : 1.938 m³/h 0.5317 kg/s

Plate heat exchanger
Heat load : 100.0 kW
.

Why would the specification give the secondary To as 50 degC, when the L8 requirement is to store/generate DHW at 60 degC? How odd that the manufacturers should choose to provide data based on temperatures that they should know to be irrelevant. If I were a cynical sort, I might suspect that they were hoping to mislead the unwary.

If the secondary To were 60 degC, the primary To would also increase and the secondary flow rate would decrease.

Does the overall efficiency include the costs of electrical energy involved in pumping the primary water through the resistance of the PHX?

 

[Dan Robinson]

Those figures are giving a delta of 45 degrees.. Nowt wrong with that (and it's in an insulated box). The 50 degree is the DHW outlet temperature with a primary inlet of 75 and a secondary inlet of 5. Primary outlet being 30.

Overall efficiencies probably don't include the pump losses, but then so what.... They will be no more than a combi boiler.

Pressure drop through the plate is thus:

Side 1 Side 2
Calculated pressure drop : 13.6 kPa 12.7 kPa

As I understand it, these figure are from the PHE manufacturers, not from the TS.



*edit -apologies I can't get the damn post to tabulate properly.

 

[Onetap]

I wouldn't fit a Vaillant again if you paid me. So frankly don't care that it can modulate. However, if a boiler is condensing with a huge delta, why worry about modulating? Modulation is for matching heat load. If the heat loads is such that modulating is not required then who cares? ?

Fine, but the point is that the OP has an Ecotec.

Now, how about a hybrid system..... an unvented cylinder reheated through a plate rather than a coil.... neat idea huh?

Been done; many commercial installations are replacing big/huge storage cylinders with a small cylinder which is heated through an external battery of PHXs, with secondary pumps dealing with the circulation from the cylinder, through the PHXs and back to the cylinder. Usually duty and stand-by PHXs, to allow for descaling.

 

[Dan Robinson]

I was thinking more along the lines of a domestic market (and yes, I know it has been done before - two companies do domestic systems that I know of).

 

[Onetap]

Those figures are giving a delta of 45 degrees.. Nowt wrong with that (and it's in an insulated box). The 50 degree is the DHW outlet temperature with a primary inlet of 75 and a secondary inlet of 5. Primary outlet being 30.

I know, but 50 degC is legionella territory, by the time you've allowed for heat losses in the distribution system. A commercial installation would have to comply with the HSE L8 document "Control of legionella.." which recommends storage at 60 degC, circulate at 50 degC (i.e., the return on a DHW circulating system). I'd HAVE to have 60 degC DHW off and I'd want a margin to allow for scaling. The PHX could deliver 60 degC, but all the other numbers would be different.

Why would they provide such odd-ball numbers in the first place?

PS I know the H&S at Work Act and L8 doesn't apply to domestic installations, but Mr. Legionella doesn't know the difference. People DO get legionella from domestic hot water systems, it just doesn't get reported.

 

[Dan Robinson]

But this is potable water, it is not stored so Mr Legionella can s0d off.

Another benefit of TS I forgot to mention.

 

[Norcon]

But there's no dhw storage with Dans plate as with combi delivery.
Its instantaneous.
Does L8 still apply? I didn't think so.

 

[Onetap]

But this is potable water, it is not stored so Mr Legionella can s0d off.

Biofilms http://en.wikipedia.org/wiki/Biofilms#Legionellosis;

Mr. Legionella and his many offspring will go forth and multiply in the distribution pipework. It's less likely with mains water, IMHO. L8 makes no distinction between mains and stored cold water supplies and I'd hope the authors knew what they were about.

PS Potable? It's all potable, has been for years. You're a long way adrift on this, I think.

Does L8 still apply? I didn't think so.

You thought wrong then. I know so.

 

[Dan Robinson]

So what happens with the thousands of Combies out there with PHE's?