ProDave

Help me find my hot water cylinder

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Trying to source my hot water tank. Usual parameter - cheapest possible.

 

Requirements

Unvented 300L capacity, separate expansion vessel (not built in due to limited height)

Input coil suitable for a heat pump.

1 immersion heater

 

In addition to the standard tank thermostat I need a separate thermostat pocket as the heat pump has it's own sensor.

 

Cylinders 2 go  are quoting £898 inc VAT and delivery

 

I am told the Telford part number is TSMI300/HP  When I search for that, this comes up https://www.mytub.co.uk/tempest-unvented-cylinder-indirect-300l-tsmi300-product-740532

 

Now that does not have the /hp on the end of the part number, but it talks about "Our standard Heat Pump coil has a surface area of 3.3m2, as a result the smallest tank we can offer is a 200litre. Smaller capacity cylinders are available where a lower surface area coil can be used."  So it seems to imply it is the heat pump version.

 

What does the panel think?

 

Assuming that is a "mistake" it seems there is a premium of about £250 extra for having the heat pump input coil, that sounds rather a lot.

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Would an external three way (2 in 1 out) heat exchanger so you could use one coil with two heat sources extra pump needed but might widen the scope. 

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The Telford cylinder does not use a heat exchange.

 

I only want 1 heat input coil but for a heat pump they specify a larger area input coil, presumably to get better conduction so the cylinder temperature will get close to the input temperature, but it seems to be adding £250 to the cost which seems rather a lot.

 

I have had a reply from my tub, they are "checking" if this cylinder really fits the description given.

 

So Telford claim the HP version of the cylinder has a 3m2 input coil, What I can't find anywhere is the surface area of the standard input coil. i.e. how much difference does it make?

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I'm lost with the price disparity TBH. 

Let me give Trevor a buzz tomorrow ;)

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Standard coil is 2.3m2, heat pump is much bigger and tappings are mid tank. 

 

Try McDonald Engineering up your way but it will be above the £1K mark. 

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1 hour ago, PeterW said:

Standard coil is 2.3m2, heat pump is much bigger and tappings are mid tank. 

 

Try McDonald Engineering up your way but it will be above the £1K mark. 

So standard tank 2.3m2 and heat pump tank 3m2 input coil.

 

I don't see the significance ot tapping heights. All I want is cold water in at the bottom and hot water out at the top. No hot water return or anything fancy.

 

Would the performance with a heat pump really be that much worse with a standard input coil?  If so in what way? slower heat up time? or hot water would not reach heat pump temperature meaning heat pump has to run at a higher temp, or more immersion boost needed to get from heat pump temp to final temp?

 

I would expect there to be a difference in price, but not almost 50% extra for the heat pump version.

 

@Nickfromwales please do make that phone call and let me know what you find out.

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By it being half way up I mean it fills half the tank - 50% more than a standard coil. 

 

And no idea about if it would work but when I spoke to Mark at Newark Cylinders last he had a tank in for a new coil for a HP as a customer “couldn’t wait” for the proper coil and he signed off a lower spec and it knackered the HP. Not a risk I want to take !

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It is like the the U-Value of a wall, the smaller the area, the less heat is transferred per unit time.  So yes, it will take longer to heat up.

The reason is that a HP has a lower output temperature, so you need more area.

 

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41 minutes ago, ProDave said:

@Nickfromwales please do make that phone call and let me know what you find out

I'll be on it like a tramp on a kebab. ;)

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I am afraid telford is not the only cylinder manufacturer that charge a premium for a heat pump cylinder. Albion, range, santon all aswell. At the end of the day its probably only a extra ten linear meter of DN 20 stainless flexible pipe in the coil length....

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You could look for a cheap indirect solar cylinder and pipe both coils together😂😂

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indirect+solar seem to have a similar premium.  Off to phone TP and Jewson for a laugh. TP don't do Telford so it will be interesting to see what they quote

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2 hours ago, ProDave said:

indirect+solar seem to have a similar premium.  Off to phone TP and Jewson for a laugh. TP don't do Telford so it will be interesting to see what they quote

Ok. As you like a deal Dave ( :ph34r: ) you can have the 300L HP UVC with the 3.3m coil for £875, OR, you can pay the £898 and Trevor will give you a £150 upgrade to the 4.5m ( iirc ) high recovery coil just mention who you are and the forum. The MyTub listing is NOT for a HP UVC, plus is more expensive for the equivalent that Trevor would supply if he was asked to provide that cylinder in that listing. They're just 3rd party re-sellers, and the mention of the HP coil in the description is just click-bait mate. 

I'm posting you a mini crowbar on next day delivery so you'll be fine to get your wallet open :D  Watch out for the Kamikaze moths !!!

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Okay, technical question. What are the advantages AND disadvantages of the larger heat input coil?

 

It is all about heat transfer and heat up times.  Bigger coil = faster heat up time?

 

BUT only if the heat pump can keep up with what the input coil can handle.

 

My heat pump is only 5KW  It's a low energy house with the max heating demand at -10 outside and 20 inside a little over 2KW so we only need a small heat pump.

 

So on the face of it the 3.3m2 coil might be the right one.  I am questioning if there is any merit in the larger one if the limiting factor may end up being the power of the heat pump?

 

And does the low power heat pump even mean the much cheaper standard input coil might be okay?

 

I can't seem to find any technical info on the "power" ratings of the various coils, and Telford have shut up shop early being a Friday so I can't speak to them until Monday.

 

Not much from other suppliers. Jewson want £926 for the Telford, and TP have offered a Gedhill for £900

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17 minutes ago, ProDave said:

It is all about heat transfer and heat up times.  Bigger coil = faster heat up time?

 

BUT only if the heat pump can keep up with what the input coil can handle.

 

Yes. Given that these things are designed to handle outputs up to 3 times what your ASHP is putting out, I suspect a standard one might be fine. However, if it's not, you're stuck with it for a long time.

 

For comparison, I have a 5kW Panasonic Aquarea with a 3.2m2 coil and have had no problems with the tank heating up quickly.

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@jack As someone with a near identical setup.

 

If you set the HP hot water temperature to (say for example) 50 degrees. How hot will the water in the tank actually get?

 

I suspect the issue is as you get close to the HP temperature the rise in temp of the HW becomes very slow and that might be where the bigger coil wins in getting the HW those last few degrees?

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If your 3.3m2 coil is stainless steel I think it would only require a temperature drop of around 3°C across it to transfer 5kW

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3 minutes ago, ProDave said:

I suspect the issue is as you get close to the HP temperature the rise in temp of the HW becomes very slow and that might be where the bigger coil wins in getting the HW those last few degrees?

 

Maybe, but that isn't what I've seen. I set mine for 55 degrees, and according to the tank stats, it gets there pretty quickly.

 

From memory, the ASHP doesn't output the target temperature while heating the tank. It outputs water that's a few degrees higher than the current return temperature. As such, you don't ever have a huge temperature difference driving energy into the tank.

 

Happy to be proved wrong about that.

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@ProDave

Were talking about £25 more for a much better coil. 

I thought it was a no brainer TBH !

I certainly can't see a disadvantage.......anyone?

 

2 hours ago, ProDave said:

I suspect the issue is as you get close to the HP temperature the rise in temp of the HW becomes very slow and that might be where the bigger coil wins in getting the HW those last few degrees?

It's what I'd go for, thus squeezing every drop of heat out. 

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Posted (edited)

Many people on this forum seem to use Telford and cylinders2go and are very happy, so I have sent you a PM.

Edited by Nickfromwales

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1 hour ago, Nickfromwales said:

@ProDave

Were talking about £25 more for a much better coil. 

I thought it was a no brainer TBH !

I certainly can't see a disadvantage.......anyone?

 

It's what I'd go for, thus squeezing every drop of heat out. 

Just wanting to make sure it's not going to try and extract heat faster than my low powered heat pump can deliver and cause some issue.  I want to run it by the technical help at Telford first.

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30 minutes ago, ProDave said:

Just wanting to make sure it's not going to try and extract heat faster than my low powered heat pump can deliver and cause some issue.  I want to run it by the technical help at Telford first.

Understood. Just a cool or cold return means you've dumped every bit of heat in that's available. A lot depends on the pump speed. 

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The kingspan ashp installation kit came with a adjustable flow meter for setting her up.

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1 hour ago, Alexphd1 said:

The kingspan ashp installation kit came with a adjustable flow meter for setting her up.

The HP installation kits seem very expensive for what they are. What did you pay and what was included if you don't mind me asking?

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Posted (edited)

Sorry I typed that sounding as i have bought  it but I am put together a diy effort from bes and eBay.  

Edited by Alexphd1
  • Thanks 1

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