aroTHERM Plus DHW Flow Temperature

[JamesPa]

2 minutes ago, sharpener said:

The problem with having a TS with HW flow through a PHX or secondary coil is there is no stratification so as you say the temp will fall steadily as you draw off.

With a coil no, but surely with a PHE between ts and dhw stratification is equally possible as with any hw tank.  Take water off at the top for the PHE, return it to the bottom.

[dpmiller]

20 minutes ago, sharpener said:

Is this a TS as just described where the temp falls, or a conventional HW cyl in which case I would expect 250l should be adequate stored volume, and 9kW input would provide a (not very generous) shower on a continous basis.

It's a TS. 3m2 HP coil at the bottom, 3m2 DHW coil at the top. There's a fair degree of stratification, I've considered a destratification pump to increase the stored energy but have never encountered a situation where it was truly necessary. I also route the UFH flow through the coil so the tank is never cold and we have some buffer volume

[Beelbeebub]

49 minutes ago, JohnMo said:

That is only true without an immersion heater. Not seen any cylinders without an immersion as a heat pump cylinder is fitted with them for legionella...

Yes, if an immersion (in fact, *especially* if an immersion is fitted) you need the full weight of the G3 regulations. Immersion heaters can and do fail on (I've dealt with 2).

 

But you don't actually need an immersion heater. A HP can achive the tank temps required for pasteurization on it's own but cannot achieve the temperatures required to boil a cylinder.

 

It would be possible to burst a tank and have a hot water leak - though a HP fed tank would normally (outside of legionella cycle) be at a much lower temp than gas fired tanks typically store at. But it would be impossible to cause the type of explosion that the regulators are worried about.

[dpmiller]

double post soz

Edited August 6, 2023 by dpmiller

[Beelbeebub]

31 minutes ago, JamesPa said:

With a coil no, but surely with a PHE between ts and dhw stratification is equally possible as with any hw tank.  Take water off at the top for the PHE, return it to the bottom.

Yes, but you need a very efficient PHX running as a counterflow HX so your outgoing DHW is at the same temp your incoming TS water is and vice versa. You also need very careful control of the pump speed. Too fast and your exit TS water is warmer than 15C (wasted capacity!) Too slow and your DHW is lower than your TS temp.

 

So theoretically a PHX system would allow you to get the same volume of DHW from a TS as a storage cylinder, but in reality you'd fall somewhat short 

[Beelbeebub]

39 minutes ago, sharpener said:

Yes but nothing to do with the heat pump per se. I would say you need to have 50l per person min at not less that 50C. One installer has quoted me some rule of thumb of (# of bedrooms + 1) x 50  as the min vol, I think this came from a cylinder mfr.

Sorry, I meant comparing TS to storage cylinder.

 

Unless you have your theoretically perfect PHX thermal store, a TS will always produce less hot water from the same volume of water at the same temp.

 

If you have lots of space then just have a bigger TS volume. If you don't mind the small hit in efficiency the use a higher temp.

[JohnMo]

3 minutes ago, Beelbeebub said:

Yes, if an immersion (in fact, *especially* if an immersion is fitted) you need the full weight of the G3 regulations. Immersion heaters can and do fail on (I've dealt with 2).

 

But you don't actually need an immersion heater. A HP can achive the tank temps required for pasteurization on it's own but cannot achieve the temperatures required to boil a cylinder.

 

It would be possible to burst a tank and have a hot water leak - though a HP fed tank would normally (outside of legionella cycle) be at a much lower temp than gas fired tanks typically store at. But it would be impossible to cause the type of explosion that the regulators are worried about.

Lots of if and buts.

 

Some HP can achieve the required temp for pasteurization, many cannot.

 

How many immersion less cylinders have you ever come across installed or being sold? If there any they are exception rather than the rule.

 

The cylinder would have to have zero provision for an immersion and happens if someone later decides to strap a willis heater on the side?

Wishful thinking that G3 doesn't need to apply.

[Beelbeebub]

3 minutes ago, JohnMo said:

Lots of if and buts.

 

Some HP can achieve the required temp for pasteurization, many cannot.

 

How many immersion less cylinders have you ever come across installed or being sold? If there any they are exception rather than the rule.

 

The cylinder would have to have zero provision for an immersion and happens if someone later decides to strap a willis heater on the side?

Wishful thinking that G3 doesn't need to apply.

The cylinders would need to be sold as "for HP only" with a big warning sticker, basically as a package with the HP (which we all know installers *love* to do! 😁). This would also solve the "only certain HP" argument.

 

The hypothetical G3-free cylinders would be packaged by the HP manufacturer as part of the system for retrofit. The bonus would be the installer wouldn't need a G3 ticket and the cylinder wouldn't need annual inspection.

 

Yes, someone could stick an external immersion on despite the warning sticker, but then that same someone could cap the PRV vent or some other stupid thing. So "someone might do the stupid thing theya rare watens not to do" is a general and not specific argument.

[JohnMo]

 

 

11 minutes ago, Beelbeebub said:

sold as "for HP only" with a big warning sticker,

Also heat pump package would have to be immersion free, nothing in the buffer, low loss header or the heat pump it's self. How do you legislate for all this. What happen in 10 years if the HP come along that boils water, throw all the old heat pump cylinders away, because they are not G3 complaint.

 

Sorry you are dreaming and not being realistic. If you don't want G3, go vented or a solution such a Harlequin cylinder or thermal store.

[Beelbeebub]

25 minutes ago, JohnMo said:

 

 

Also heat pump package would have to be immersion free, nothing in the buffer, low loss header or the heat pump it's self. How do you legislate for all this. What happen in 10 years if the HP come along that boils water, throw all the old heat pump cylinders away, because they are not G3 complaint.

 

Sorry you are dreaming and not being realistic. If you don't want G3, go vented or a solution such a Harlequin cylinder or thermal store.

I'm not suggesting the cylinders don't have G3 features like prvs etc.

 

IMHO, we are somewhat overcautious when it comes to invented cylinders.  The design of the cylinders, and in particular the safety group, *is* important.

 

But it is by and large done by prepackaged devices that are matched to the cylinder at manufacture.

 

The requirements for G3 "tickets".and annual inspection seems a little over the top given there is actually nothing the inspection does. It's basically a visual check and a check of the expansion vessel. So there may be a small benefit to relaxing the regulations in the context of HP.installs.

 

But it's fairly moot, to G3 or not to G3 is a pretty small issue in the grand scheme and the potential to drop it in certain limited.circumstance is a.footnote.

Edited August 6, 2023 by Beelbeebub

[JamesPa]

10 hours ago, Beelbeebub said:

Yes, but you need a very efficient PHX running as a counterflow HX so your outgoing DHW is at the same temp your incoming TS water is and vice versa. You also need very careful control of the pump speed. Too fast and your exit TS water is warmer than 15C (wasted capacity!) Too slow and your DHW is lower than your TS temp.

A bit of control electronics to modulate the pump speed.  If a cylinder can run Linux (mixergy, alledgedly) then a simple control of pump speed is certainly possible.

 

Also how much does it matter if the hot water is hotter than target, it simply gets mixed down at the outlet as we currently do so you use less in proportion.

 

My gut feel is that getting the stratification right is more important than getting the output temp spot on.

9 hours ago, Beelbeebub said:

Unless you have your theoretically perfect PHX thermal store, a TS will always produce less hot water from the same volume of water at the same temp.

 

If you have lots of space then just have a bigger TS volume. If you don't mind the small hit in efficiency the use a higher temp.

Clearly the thermodynamics means this is the case.  But a TS can have a rectangular footprint giving 27% more volume for the same useful floorspace.

 

The Harlequin stores are interesting and do appear to have been adopted by RED.  However I'm not sure how relevant that is as I can't see any evidence RED are actually doing anything.  Maybe I have missed something.

 

I wish I had a lab to run some experiments!

[sharpener]

Has anyone found a complete description of how the Harlequin works?

 

From reading here and (scant info on) H web site it seems they have one coil at the bottom to input heat and another at the top for DHW flow to abstract it in real time. If the water cooled by the latter falls to bottom of tank without mixing then there will be stratification and you will get hot water at constant temp until the cold level reaches top coil.

 

If so what is the gubbins on top of the tank (flexi-hoses, solenoid valve are visible), how does the ?stagnant body of water keep free of nasties, what are the different overfill options referred to?

 

H are a longstanding mfr of (polythene) oil tanks etc so this looks like a logical diversification for them. Polypropylene has been used for washing machine tubs for many years so should be an appropriate material to use for the inner and an interesting change from metals.

[JohnMo]

.

10 minutes ago, sharpener said:

Has anyone found a complete description of how the Harlequin works?

 

You have a body of water in the cylinder it is static.

 

The heat pump cylinder has a 20.1m long 20mm coil from bottom to top of cylinder of heating - coil is twice as long as their normal cylinder.

 

There is a second coil for heating DHW from bottom to top of cylinder again 20mm dia but about 10m long 

 

The immersion heater and thermostat are accessed from top of cylinder.

 

Cold in and hot out are at top of cylinder, as is the cylinder filling loop. There is also a mixing valve set to temper water temp.

 

Not a lot different from a thermal store

 

Overflow you can overflow to catch tank or to a drain in case of overfilling

[Beelbeebub]

1 hour ago, JamesPa said:

A bit of control electronics to modulate the pump speed.  If a cylinder can run Linux (mixergy, alledgedly) then a simple control of pump speed is certainly possible.

 

Also how much does it matter if the hot water is hotter than target, it simply gets mixed down at the outlet as we currently do so you use less in proportion.

 

My gut feel is that getting the stratification right is more important than getting the output temp spot on.

Yes, but I wouldn't underestimate the difficulty of getting the pump speed control just right when you get into the real world of sensor lag, pump flow rate floors, varying temp inputs and flow rates etc. The pump to control all that would be at least the same as an off the shelf pressure boost pump but not off the shelf.

 

Here's my thought process

 

The tank for the thermal store and the vented cylinder are more or less the same thing, so the argument "you can do X" to one applies to the other i.e it's a tie between the two systems in this area

 

If you use a PHX both need a pump (boost pressure or feed PHX) but the vented cylinder pump is off the shelf whilst the TS + PHX pump is more bespoke. So advantage VC

 

The vented cylinder needs a ball valve, feed tank etc, relatively simple and cheap, the TS needs a PHX, simple and fairly commodity, so I'd say a tie.

 

The VC wins on efficiency (as we discussed). The TS can approach the VC on this front but only at the expense of complexity. On the plus side for the TS, you wouldn't need to do legionella cycles.

 

For the TS, stratification is absolutely key. Without it, your efficency drops relative to VC. For VC, stratification is also important but easier to achieve.

 

And.yes, experiments would be great!😀 

 

It's entirely possible the differences in prices and performance are fairly negligible so the decision is down to other things like availability, space, exact circumstances etc

Edited August 7, 2023 by Beelbeebub

[sharpener]

1 hour ago, JohnMo said:

The heat pump cylinder has a 20.1m long 20mm coil from bottom to top of cylinder of heating - coil is twice as long as their normal cylinder.

 

There is a second coil for heating DHW from bottom to top of cylinder again 20mm dia but about 10m long 

 

How does that give you stratification then?

 

BTW @JohnMo did you see my latest on this thread?

 

Edited August 7, 2023 by sharpener

[JamesPa]

2 hours ago, Beelbeebub said:

It's entirely possible the differences in prices and performance are fairly negligible so the decision is down to other things like availability, space, exact circumstances etc

All of which illustrates the madness of being forced by the industry to swap out a working system!

 

There is, I think we can safely conclude, no perfect solution so the best one is probably the one you have already.

[markocosic]

Thermal stores with coils in have lousy available capacity per unit of stored water.

 

I think their main advantages are the lack of discharge; and being able to use the bottom of them as a buffer for the space heating / heat pump defrosting.

[Beelbeebub]

1 hour ago, markocosic said:

Thermal stores with coils in have lousy available capacity per unit of stored water.

 

I think their main advantages are the lack of discharge; and being able to use the bottom of them as a buffer for the space heating / heat pump defrosting.

Yes. Especially if the storage temp is very low, which you want it to be for HPs 

 

I think that's why UVCs (with or without G3!😁) Will probably be the default.  They are fairly widely used now anyway.

 

The alternative is the vented cylinder, but that may need a pressuring pump. The pump would make it directly comparable to a UVC, but may net be needed, there are quite a few places that operate on VC's at the moment.

 

Or you could have direct on demand electric hot water, this is definitely a possibility if you don't need a bath filling eg small flats. 

Edited August 7, 2023 by Beelbeebub

[dpmiller]

Yep, the Heatstream is just a TS. I was aiming for one prior to Harlequin pulling them off retail sale, and had our TS configured in a similar fashion.

 

The Heatstream looks busy on top because it's got the mixing valve and a filling loop all up there. It's manual-fill-to-overflowing, with an air gap above, and a nifty wee float indicator for the level. Plus a possible 3rd coil for an additional heat source.

 

 

Bear in mind, all you that poo-poo the lack of stored volume of the HS or other thermal store, that here in NI a small cylinder with a Willis is absolutely the norm and people are used to the concept of charging and re-charging a cylinder with heat. A 6-9kW HP can do much more than a 3kW Willis

 

 Copper Industries also approximated the idea in their Maxi-Pod tank

[Beelbeebub]

The thing about Willis heaters (and any immersion heater) is they produce high temp water, so the effective volume of the cylinder is way higher when it delivers water at 45C.

 

With direct electric there is no penalty for providing high temperature. 3kwh is 3kwh regardless of it being lots of 40C water or less 80C water at 100% efficiency.

 

Electric tanks always store water at +65C

 

So your 120l vented tank at 65C gives way more like 160l or 180l of 45C bath water.

 

You can do that with a HP, but at a penalty. So storing at 45C is the lowest you can go, and your 120l cylinder that was ok on electric is a bit too small on a HP. (Except after the legionella cycle!)

[JamesPa]

39 minutes ago, dpmiller said:

Bear in mind, all you that poo-poo the lack of stored volume of the HS or other thermal store, that here in NI a small cylinder with a Willis is absolutely the norm and people are used to the concept of charging and re-charging a cylinder with heat. A 6-9kW HP can do much more than a 3kW Willis

That's really interesting.  I had begun to ponder some while ago whether differences in dhw practice might contribute materially to the UK VS EU disparity in heat pump deployment (obviously government vacillation and electricity/gas price ratios are the major contributors).  You are now telling us that there is a potentially significant NI Vs England disparity.  

 

It seems 'we' 'expect' ideal DHW provision sufficient to allow two long haired teenage daughters and sundry other members of the family to shower each morning in quick succession for 10 minutes each.  That's a level of luxury we have no right to expect, and regulations for all shouldn't be based on it.

 

'Teenage girls (or boys) block fixing climate change' is a headline I don't expect to see, but there may be a grain of truth in it nevertheless!

 

Seriously though, is it possible that our dhw expectations are unreasonable relative to practices in other European countries/regions?

 

Basically I am now concluding that the 5K subsidy is paying for MCS (about 1.2K according to one price list I have seen), a frequently unnecessary (with R32/290 heat pumps) DHW 'upgrade' and, sadly, in too many cases, price gouging, leaving a negative amount for the consumer.  Until this changes heat pumps will remain niche and climate change will get worse.

Edited August 7, 2023 by JamesPa

[JohnMo]

The Willis site is an interesting read, and the whole concept of heating water. You want a shower in half you flick the switch, willis heater add heat from the top down and you heat just water in the cylinder.

 

We seem ok with with dumping 1.5kWh into the house in heat loss every day of the year to have a hot cylinder 24-7 on demand.

 

Would suspect, the Willis heater used as designed would be very economical to run.

[JamesPa]

50 minutes ago, JohnMo said:

We seem ok with with dumping 1.5kWh into the house in heat loss every day of the year to have a hot cylinder 24-7 on demand.

Complex equation.  During the heating season the heat is not wasted (assuming that the cylinder is within the heated envelope).  Outside the heating season it is, possibly doubly so if you invoke cooling.  However many use the 'waste' heat to create an 'airing cupboard' (also good for proving dough) and would be unhappy if this facility were removed.

 

On the other hand you can add pipe losses, eg filling my kitchen sink has a COP of 0.5 because I waste as much in the pipes as I put in the sink, due to the circuitous route the plumbing takes.

 

Point of use heaters, possibly with a small amount of local storage, are really not so bad for anything other than showers or baths, in fact if it weren't for showers and baths I doubt we would bother with dhw storage at all.  In the community buildings that I have converted to ashp that's the way we have gone, because there is no requirement for showers/baths and it circumvents all the legionella faff.

 

For baths you can wait a bit longer if the water is heated slowly (as our grandparents did when they heated a bathtub in front of the fire).  It's really only showers that depend on significant amounts of dhw delivered at speed in real time. 

 

Aerated or 'eco' shower heads, a few tens of £ to purchase, reduce the water required and purport to give a satisfying experience.  I do wonder whether working on the demand side would make the supply side a lot easier and be a good investment for both the country and individuals.

 

Perhaps we are just aiming unnecessarily high with our 250l+ tanks and a 30-60 min recovery.  Is this really necessary and how many costal cities/low lying countries is it worth sacrificing, for this luxury?

 

 

[Beelbeebub]

How about, storing water in a pressurised TS (basically a buffer vessel) at whatever the CH flow temp is, or maybe a touch above. Anything from mid 20's.  This can also act as the buffer to avoid cycling and the defrost volumiser.

 

Then via a simple coil you preheat the hot water circuit to whatever temp the buffer/TS can manage before sending it on to the instantaneous heater unit. 

 

If incoming mains is 15C and you want your shower at 45C that's a 30C rise or 3.5-5lpm

 

But if you manage to preheat the water to 25C it's only 20C and you can achive 5-8lpm. 

 

If your buffer/volumiser is at 35C, then even you're talking 8lpm even for a weedy 7.5kw shower

 

[dpmiller]

then add a drain HE too