Design Help - Plumber not helping

[Nickfromwales]

Lost track of this one. 

My point about the instant is that your dropping down from a 22mm outlet from the UVC and then have the 15mm inlet / outlet of the instant. There will be a drop in performance there without a doubt, how much exactly will be down to the unit, but  it is a definite design consideration. 

Also, I'd be VERY interested as to what the Steibel unit will produce as useful heat at anything over 10/12 litres per min with cold water going in.  @JSHarris, can you add some details if possible please? Ta. 

On 07/03/2017 at 14:34, DeeJunFan said:

@Nickfromwales

 

So you would suggest get rid of the back boiler.  Get rid of the In-line instant at the tank and go 300L TS fed from ASHP and 300L UVC pre-heated from the ASHP TS Coil and topped up by Solar PV/Immersion.

 

Backup plan would be Direct Electric Immersion to top up temps.

In a nutshell yes. 

With a possible 12kw of direct electric heating ( 4 x 3kw immersions @ 2 per tank ) I seriously doubt you'll ever need a back up on the back up. By all means fit a cable for an electric instant, but I'd hold off buying and fitting one unless it's needed.

Plumb both cylinder to the ASAP ( low grade heat to the TS and high grade heat to the UVC. UVC selected as manual boost only for when pv isn't generating ). It would be, imo, madness not to as you'll have oodles of DHW, a backup plan in case the ashp goes down / off for maintenance, and most of your DHW supplied at the better range of CoP from the ashp. 

 

[Jeremy Harris]

2 hours ago, Nickfromwales said:

Lost track of this one. 

My point about the instant is that your dropping down from a 22mm outlet from the UVC and then have the 15mm inlet / outlet of the instant. There will be a drop in performance there without a doubt, how much exactly will be down to the unit, but  it is a definite design consideration. 

Also, I'd be VERY interested as to what the Steibel unit will produce as useful heat at anything over 10/12 litres per min with cold water going in.  @JSHarris, can you add some details if possible please? Ta.

 

 

Instant water heaters are near enough 100% efficient, in terms of calculating the temperature rise for any given flow rate and temperature differential, but as there are two variable here, then both need to be known to calculate the temperature rise. 

 

Some examples, given as a temperature differential for a range of flow rates, for the 9.6 kW maximum unit we have:

 

5 litres/minute = 27.3 deg C rise

6 litres/minute =  22.7 deg C rise

7 litres/minute =  19.5 deg C rise

8 litres/minute =  17.1 deg C rise

9 litres/minute =  15.2 deg C rise

10 litres/minute =  13.6 deg C rise

11 litres/minute =  12.4 deg C rise

12 litres/minute =  11.4 deg C rise

13 litres/minute =  10.5 deg C rise

14 litres/minute =  9.7 deg C rise

15 litres/minute =  9.1 deg C rise

 

This illustrates well just how much power you need to heat water to a reasonable temperature with an instant heater, and why electric showers can only deliver a pretty low flow rate (typically less than 5 litres/minute) compared with a shower heated by something like a decent combi boiler, with 30 kW of more of instant heating power available.  For a low energy house, where tank heat loss can be a nuisance in summer (as our old thermal store proved to be) there is some merit in looking using a low temperature warm water tank, say, around 35 to 40 deg C (plus an anti-legionella boost every couple of weeks to 60 deg C) and then just using instant heaters to boost this warm water to, say, 50 to 55 deg C on demand.  The losses of such a system are a lot lower; a tank at 40 deg C in a house that's at 20 deg C will have half the heat loss of a tank at 60 deg C in the same house, for example. 

 

In our specific case, the pre-heated incoming cold supply can drop to about 29 deg C before the instant water heater can no longer deliver 42 deg C at 10 litres/minute, about the lowest acceptable shower temperature and flow rate for us.  This means we can squeeze more useful heat from both the Sunamp PV heat battery and the 70 litre buffer tank, as the combined output from both can drop to around 15 deg C lower than would be acceptable for a shower, because of the added boost from the instant water heater.

 

Edited to add: Thanks for the edit, Nick.  Whatever was in that big blank space at the bottom just wouldn't delete for me, no matter what I tried

Edited March 10, 2017 by JSHarris
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[joe90]

All very useful info. The only problem with backup from immersions is the wait!, get undressed for a shower and oops will have to wait xxx minutes before I can wash. Also using an instant water heater you heat the exact amount of water you require not a whole tank full which may or may not be used soon. I don't think it will be possible to predict until we get to use the house in anger but whether it's economical or not to have E7.

Edited March 10, 2017 by joe90
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[DeeJunFan]

12 hours ago, Nickfromwales said:

Lost track of this one. 

My point about the instant is that your dropping down from a 22mm outlet from the UVC and then have the 15mm inlet / outlet of the instant. There will be a drop in performance there without a doubt, how much exactly will be down to the unit, but  it is a definite design consideration. 

Also, I'd be VERY interested as to what the Steibel unit will produce as useful heat at anything over 10/12 litres per min with cold water going in.  @JSHarris, can you add some details if possible please? Ta. 

In a nutshell yes. 

With a possible 12kw of direct electric heating ( 4 x 3kw immersions @ 2 per tank ) I seriously doubt you'll ever need a back up on the back up. By all means fit a cable for an electric instant, but I'd hold off buying and fitting one unless it's needed.

Plumb both cylinder to the ASAP ( low grade heat to the TS and high grade heat to the UVC. UVC selected as manual boost only for when pv isn't generating ). It would be, imo, madness not to as you'll have oodles of DHW, a backup plan in case the ashp goes down / off for maintenance, and most of your DHW supplied at the better range of CoP from the ashp. 

 

 

I had no idea you could Plumb the ASHP to 2 different tanks.  I take it there will be some kind of valve to switch the flow to the UVC once the temp of the ASHP is increased. 

 

I was planning the TS on first floor and the UVC in the attic so will have to see if that plan still looks OK without the bonus of getting heat from the back boiler. 

 

 

[le-cerveau]

You can set most ASHP's to provide low grade heat (UFH, buffer tank) and High Grad Heat (DHW), it will have the facility to operate a valve to say where the heat is going depending on the demand, so plumb your UVC in as the DHW circuit and the TS as the UFH buffer tank.  This a facility of most modern ASHP's.

[Nickfromwales]

9 hours ago, DeeJunFan said:

I had no idea you could Plumb the ASHP to 2 different tanks.  I take it there will be some kind of valve to switch the flow to the UVC once the temp of the ASHP is increased. 

 

It's no different to how a regular heating and hot water system is plumbed. The heat source ( ASHP ) produces heat, and it gets pumped out. That flow goes to a diverter valve which has 3 ports.....

1) heated water in from HP

2) flow to UFH / buffer

3) flow to DHW / uvc

When the demand is for Ufh, the unit idles at low temp / max CoP, but when the UVC calls for heat ( cyl stat and / or 'boost' controller ) then flow to the Ufh is completely isolated and the HP ramps up to say 55oC to heat the UVC only. When the UVC is up to target temp, the diverter redirects flow away from the UVC, back to the Ufh, and lowers the temp accordingly. 

The ashp gets a trigger signal, either from the 3 port valve or cyl stat, so it knows when to alter the temp range. 

[PeterW]

I'm doing just this with a classic W Plan scheme. 

 

My ASHP needs an inline temp stat to control the max flow so I have one in one side of the diverter valve at 32c and one in the other at 48c. 

[Jeremy Harris]

4 hours ago, le-cerveau said:

You can set most ASHP's to provide low grade heat (UFH, buffer tank) and High Grad Heat (DHW), it will have the facility to operate a valve to say where the heat is going depending on the demand, so plumb your UVC in as the DHW circuit and the TS as the UFH buffer tank.  This a facility of most modern ASHP's.

 

 

You can do this, and our ASHP has a DHW setting, via dry contacts or the programmer, so that it can receive a call for DHW and increase the flow temperature to 55 deg C.  In practice you're better off using an immersion heater during the cooler, damper, months, though, as the ASHP runs around three or four defrost cycles per hour in cool, damp, weather and the real-world COP (not the highly optimistic dry air COP often quoted) drops to close to unity. 

 

I ran a lot of experiments with our ASHP, to try and understand how it worked.  Ours has an outside air temperature sensor and a humidity sensor and uses these to determine when there is an icing risk and when to run a defrost cycle.  When defrosting it goes into cooling mode, drawing heat from the house or hot water system to warm up the heat exchanger and melt any ice.  A typical defrost cycle takes around 10 minutes, so any more than three defrost cycles per hour takes you into the region where the real world COP is at unity or below.  The main factor seems to be humidity, rather than just air temperature, so the worst performance isn't in cold weather, it's in cool, wet, weather.  Sadly, we seem to get a fair number of days in autumn, winter and spring where the humidity is high enough to cause a problem.

 

The solution was to not use the DHW capability of the ASHP and set it to a maximum flow temperature of 40 deg C.  At this flow temperature it never seems to need to defrost when meeting our pretty low heat demand, so always gives a pretty good COP, better than the published data would suggest most of the time, I think.

 

The best solution for heating an DHW from an ASHP seems to be to use a hybrid, like the Daikin Altherma.  They use the ASHP part for pre-heating DHW and running the heating system, with a gas combi to boost the DHW.  The big advantage is that one of these uses much less gas than a conventional combi system, because most of the "heavy lifting" is down by the heat pump taking the water to within about 15 deg C of the required DHW temperature, so it is a reasonable option for running from LPG.

[DeeJunFan]

On 11/03/2017 at 09:07, Nickfromwales said:

It's no different to how a regular heating and hot water system is plumbed. The heat source ( ASHP ) produces heat, and it gets pumped out. That flow goes to a diverter valve which has 3 ports.....

1) heated water in from HP

2) flow to UFH / buffer

3) flow to DHW / uvc

When the demand is for Ufh, the unit idles at low temp / max CoP, but when the UVC calls for heat ( cyl stat and / or 'boost' controller ) then flow to the Ufh is completely isolated and the HP ramps up to say 55oC to heat the UVC only. When the UVC is up to target temp, the diverter redirects flow away from the UVC, back to the Ufh, and lowers the temp accordingly. 

The ashp gets a trigger signal, either from the 3 port valve or cyl stat, so it knows when to alter the temp range. 

 

OK I will need to check how I'm fixed for that I bought anew ASHP on eBay about 2 months the ago and it said heating only so not sure if it does the higher Temps but it doesn't offer cooling.  I know I could like you make it but I wouldn't have the capability to get into it. 

 

If the ASHP has a max temp not much more than 40 would I just go the previous route of plumbing it into the TS for UFH and have the cold after uplifted through the TS coil for the UVC?

 

If the UVC was always getting where in at 40 then hopefully we wouldn't need a lot of direct electric to boost it up.

[PeterW]

5 hours ago, DeeJunFan said:

 

OK I will need to check how I'm fixed for that I bought anew ASHP on eBay about 2 months the ago and it said heating only so not sure if it does the higher Temps but it doesn't offer cooling.  

 

Which one have you got ..?? Is it one of the Ice Energy ones ..?

[Nickfromwales]

19 hours ago, DeeJunFan said:

If the UVC was always getting where in at 40 then hopefully we wouldn't need a lot of direct electric to boost it up.

Legionella purge would need doing weekly. If you set up a timer for the last hour of E7 then that would stay warm ( hot ) for the morning showers so wouldn't be 'wasted' ( heated high for purging then left to ebb away back to idle temp ). 

Fact is, with a pv based immersion it's likely that you'd be achieving high enough temps to purge at midday every day, but unless it was logged and automated then you'd still need a failsafe e.g. a timer on grid electric. If you only had a single immersion you could just mount that timer to bridge the pv diverter ( immersun / other ). 

 

[vfrdave]

On 11/03/2017 at 10:55, JSHarris said:

like the Daikin Altherma.  They use the ASHP part for pre-heating DHW and running the heating system, with a gas combi to boost the DHW.

Grant engineering now do a hybrid asap and oil boiler probably more suitable for the NI market where much of rural NI have no mains gas. They had it on display at the show, I'm waiting on more detailed information coming through from their technical department.

[JamieM]

13 hours ago, vfrdave said:

Grant engineering now do a hybrid asap and oil boiler probably more suitable for the NI market where much of rural NI have no mains gas. They had it on display at the show, I'm waiting on more detailed information coming through from their technical department.

 

be sure to post up about this as i would have an interest in this route too.

 

cheers

[Nickfromwales]

13 hours ago, vfrdave said:

Grant engineering now do a hybrid asap and oil boiler probably more suitable for the NI market where much of rural NI have no mains gas. They had it on display at the show, I'm waiting on more detailed information coming through from their technical department.

Can you start a new topic for that when the time comes please Dave 

Thanks. 

[Barney12]

18 hours ago, vfrdave said:

Grant engineering now do a hybrid asap and oil boiler probably more suitable for the NI market where much of rural NI have no mains gas. They had it on display at the show, I'm waiting on more detailed information coming through from their technical department.

 

+1 Sounds V interesting!

[vfrdave]

@Nickfromwales Promise I will start a new topic when or if I get more details.  In the mean time @Barney12 and @JamieM here is a link to the VortexAir Hybrid with some basic information.

[DeeJunFan]

On 3/11/2017 at 20:46, PeterW said:

 

Which one have you got ..?? Is it one of the Ice Energy ones ..?

Yes I think so.

 

Any horror stories?

[DeeJunFan]

On 3/13/2017 at 13:27, vfrdave said:

@Nickfromwales Promise I will start a new topic when or if I get more details.  In the mean time @Barney12 and @JamieM here is a link to the VortexAir Hybrid with some basic information.

 

Did they talk money?

[PeterW]

6 hours ago, DeeJunFan said:

Yes I think so.

 

Any horror stories?

 

None that I am aware of ..! They use a simple pipe stat to regulate the water temperature - I've come up with a change over relay scenario that when the 3 way valve changes over then it also connects a relay to move from a low temp 35c stat to a high temp 47c stat. That allows me to have dual flow temps. 

[vfrdave]

8 hours ago, DeeJunFan said:

 

Did they talk money?

Nothing concrete that I would be prepared to quote them on.

[Jeremy Harris]

4 hours ago, PeterW said:

 

None that I am aware of ..! They use a simple pipe stat to regulate the water temperature - I've come up with a change over relay scenario that when the 3 way valve changes over then it also connects a relay to move from a low temp 35c stat to a high temp 47c stat. That allows me to have dual flow temps. 

 

Worth looking at the ASHP controls, as you may find that it has a DHW setting.  Ours has, there's a dry contact for heating and a separate dry contact for DHW.  The temperatures for both are set by the ASHP command unit programming, so you can set a weather compensated heating flow temp if you like (there are various preset curves, plus the option to define your own custom curve) and you can set the DHW temperature when it's in DHW mode.  All you need do then is use a valve operated microswitch to select the DHW or heating contacts, as required.

[DeeJunFan]

So our first choice plumber has become unresponsive.

 

Took the plunge and engaged another one and this time the guy has experience of installing ASHP and MHRV so i'm hoping he actually knows something about them and not just a bandwagon jumper.

 

First phone call went something like.  

 

Me: I was thinking of going the 2 tank system, one for UFH heated by the ASHP and a second DHW tank heated by pre-heat from ASHP and Immersion (PV & Direct Electric).  50/50 on stove with back boiler

Plumber: I wouldn't bother with 2 tanks just plumb the ASHP directly into the UFH Manifolds and then have the pre-heat going into 1 DHW tank.  He recommended going TS for the tank, in the case of additional heat sources.  But advised on going just room heater for the stove.

 

Asked for plans and would put together a proposal.  Haven't got that yet but what do you think about the first comments?  @Nickfromwales

[Nickfromwales]

For the grief with the stove installation, unless you intend to use it a lot, I'm with him. 

I completely disagree with him about driving the preheat into the DHW tank as that's nonsense. If your Pv is generating at all, then your likely UVC ( proposed TS ) temp will reside ABOVE the low grade temp range of the ashp 'pre-heat' ( aka high CoP ) yield, so basically you'll be COOLING the cylinder with the ashp and that's obviously not the way forward. The only way to link the ashp to the DHW tank is to accept the hit on the CoP and drive it at 55oC. Essentially with your new guys proposal you'd never get the ashp to supply any heat to the TS unless it was switched on from cold.  As it would prob never get that cold it'll never ask for low grade heat input. 

Regards to the recommendation for the TS instead of the UVC then it's a bit too difficult to just say it's a good / bad idea. The primary tank for low grade ( in previous chat ) would sit at a temp low enough to not give masses of unwanted latent heat loss, but will then allow you to reduce the size of the UVC. The UVC will be the tank with the higher, possibly nuisance, latent heat loss so that's the one to focus on. If you change to a multi input single TS, it'll be very high temp ( 70+oC ) and it'll need to be a biggy. More losses, less efficient, more ( *) connective pipework to leak heat away, and zero opportunity to preheat ANY DHW from the ashp,  ( * ask @Declan52 about the importance of keeping the pipework related losses under control for real life feedback  ), plus you'll need to keep boosting it with electricity to max out the correct temp, as, even at 55oC, the ashp is not at all suited to directly and singularly running a TS. ( IMO ). 

Pointless in going to the efforts you have done with insulation / airtightness etc and then have a horribly inefficient heating and DHW system. 

Sorry for the headaches 

 

[DeeJunFan]

23 minutes ago, Nickfromwales said:

For the grief with the stove installation, unless you intend to use it a lot, I'm with him. 

I completely disagree with him about driving the preheat into the DHW tank as that's nonsense. If your Pv is generating at all, then your likely UVC ( proposed TS ) temp will reside ABOVE the low grade temp range of the ashp 'pre-heat' ( aka high CoP ) yield, so basically you'll be COOLING the cylinder with the ashp and that's obviously not the way forward. The only way to link the ashp to the DHW tank is to accept the hit on the CoP and drive it at 55oC. Essentially with your new guys proposal you'd never get the ashp to supply any heat to the TS unless it was switched on from cold.  As it would prob never get that cold it'll never ask for low grade heat input. 

Regards to the recommendation for the TS instead of the UVC then it's a bit too difficult to just say it's a good / bad idea. The primary tank for low grade ( in previous chat ) would sit at a temp low enough to not give masses of unwanted latent heat loss, but will then allow you to reduce the size of the UVC. The UVC will be the tank with the higher, possibly nuisance, latent heat loss so that's the one to focus on. If you change to a multi input single TS, it'll be very high temp ( 70+oC ) and it'll need to be a biggy. More losses, less efficient, more ( *) connective pipework to leak heat away, and zero opportunity to preheat ANY DHW from the ashp,  ( * ask @Declan52 about the importance of keeping the pipework related losses under control for real life feedback  ), plus you'll need to keep boosting it with electricity to max out the correct temp, as, even at 55oC, the ashp is not at all suited to directly and singularly running a TS. ( IMO ). 

Pointless in going to the efforts you have done with insulation / airtightness etc and then have a horribly inefficient heating and DHW system. 

Sorry for the headaches 

 

 

No need to apologise, this is kind of the whole point.

 

So fresh slate.

 

Forgetting the stove and just accounting for the ASHP and PV.

 

Best option.  Your back of a napkin design if thats ok @Nickfromwales

[joe90]

I am following this thread (as best I can) because some of my situation is the same, I.e. ASHP but no PV. From previous threads I came to the decision to use an UVC DHW cylinder ( very well insulated) at a modest temperature because ( and correct me if I am wrong) this type of cylinder can give almost the whole tank of hot water till it runs out but a thermal store will give cooler water as it is depleated therefore not consistent "hot" temp.

Edited March 22, 2017 by joe90
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