When the UFH flow Temp is <35C, dhw?

[Post and beam]

Following on from my other thread about my concerns with a potential installer.

 

How does the ASHP deal with heating the DHW to a suitable temperature? i guess it runs for a short period at 50 ish degrees and then reverts if required to the lower flow rate for the floor. If correct then we need some hours in the day free from UFH heating to do this job.

 

Have i understood it well enough?

[JohnMo]

So the way it works is 

 

DHW is priority, it is heated via thermostat or temperature probe and an adjustable hysterisis and or timer within the ashp controller.

 

We have a 6kW heat pump and a 210L cylinder, our reheat time is between 45 and 60 mins, and we heat in timed slots 7am to 8.30am and 2pm to 3pm. It almost always heats at 7am, sometimes at 2pm.

 

All other time is for house heating.

 

Switching between the two services is via a 3 port valve. The ASHP automatically adjusts flow temps.

[Post and beam]

High JohnMo

Perfect, thanks. Just as i thought really and totally negates the 45 degree UFH flow temp nonsense i have been arguing with what i thought was my chosen installer. Both halves of the system at the same temperature was their mantra.

[Beelbeebub]

19 minutes ago, Post and beam said:

High JohnMo

Perfect, thanks. Just as i thought really and totally negates the 45 degree UFH flow temp nonsense i have been arguing with what i thought was my chosen installer. Both halves of the system at the same temperature was their mantra.

Thats daft and uneccesary as you have to put in a valve for switching between DHW and heating anyway, so why would you design the heating temp to be higher than it needs to be? 

 

That sort of thinking sharks back to (old) gas boiler days when you only had one flow temp so set it based on DHW (usually over 65C) and then designed the heating system around that temp. 

 

If your installer is using that logic you need a different installer. 

[marshian]

13 minutes ago, Beelbeebub said:

Thats daft and uneccesary as you have to put in a valve for switching between DHW and heating anyway, so why would you design the heating temp to be higher than it needs to be? 

 

That sort of thinking sharks back to (old) gas boiler days when you only had one flow temp so set it based on DHW (usually over 65C) and then designed the heating system around that temp. 

 

If your installer is using that logic you need a different installer. 

 

Reminds me of my neighbour - He had a Viessman 100W Heat only boiler fitted - with weather compensation but not DHWP - consequently his flow temp is fixed for CH at 68 deg (Because any lower than that and his HW is not heated in a reasonable time) totally negates the point of weather compensation because the boiler isn't actually using it despite there being an outside temp sensor on the north facing wall.

 

At the end of the day he's got a nice boiler but he's not taking any advantage of what it can do when the temperatures aren't -2

[JamesPa]

42 minutes ago, Beelbeebub said:

That sort of thinking sharks back to (old) gas boiler days when you only had one flow temp so set it based on DHW (usually over 65C) and then designed the heating system around that temp. 

 

If your installer is using that logic you need a different installer. 

Are plumbers required/encouraged to undertake cpd.  If not clearly they should be!

[SteamyTea]

1 hour ago, JamesPa said:

Are plumbers required/encouraged to undertake cpd.  If not clearly they should be!

Yes they should, but most CPD I have done (as a teacher/lecturer) was very low quality.

[sharpener]

2 hours ago, marshian said:

 

Reminds me of my neighbour - He had a Viessman 100W Heat only boiler fitted - with weather compensation but not DHWP - consequently his flow temp is fixed for CH at 68 deg (Because any lower than that and his HW is not heated in a reasonable time) totally negates the point of weather compensation because the boiler isn't actually using it despite there being an outside temp sensor on the north facing wall.

 

At the end of the day he's got a nice boiler but he's not taking any advantage of what it can do when the temperatures aren't -2

 

I had a boiler installed in 2010, the installer (subcontractor to loft conversion ppl) had never heard of WC, I specified a Vokera bc it was the smallest I could find with WC but he had no idea how to wire it. I consulted Vokera technical who said to fit an external relay to inhibit the WC when HW calls for heat. Not a neat solution, they could easily have put a HW demand input on the pcb at no cost to themselves.

 

Even so there is no independent setting of the flow temps, if you want to increase the WC curve it also increases the HW temp.

[marshian]

3 hours ago, sharpener said:

 

I had a boiler installed in 2010, the installer (subcontractor to loft conversion ppl) had never heard of WC, I specified a Vokera bc it was the smallest I could find with WC but he had no idea how to wire it. I consulted Vokera technical who said to fit an external relay to inhibit the WC when HW calls for heat. Not a neat solution, they could easily have put a HW demand input on the pcb at no cost to themselves.

 

Even so there is no independent setting of the flow temps, if you want to increase the WC curve it also increases the HW temp.

 

I had my 100W (Heat only) fitted by a Viessmann trained Gas Engineer at the end of July

 

I was really specific about what I wanted and how I wanted it set up (not specific enough in hindsight)

 

Hopefully the HW demand box, the Wifi Module and the NO CH zone valve (to replace the NC zone valve that was fitted) will all get fitted very soon then I can turn on the weather compensation and the CH can do it's CH thing based on a the WC curve and the HW I can set up to do it's thing at an elevated flow temp in a reasonable time frame.

 

Once it's all sorted I might do a little thread on it. It does amaze me how low the Viessman can go in terms of flow temp and output.

[Dave Jones]

our setup similar to johnmo, albeit we control all automation with home assistant. Heat pump is always on automatic 24x7 either for cooling or heating. hot water replenishes to 40 via ASHP immediately, then depending on the time of day (solar availability) it checks the 30min octopus price for cheapness and if its cheap it blasts to 55 after which the eddi (ASHP has no direct control of the immersion) takes it to 65.

 

Took  a bit of tuning to get setup but now its just set and forget.

[MikeSharp01]

I looked at the Viessman units as they have a 4kW mono block which has a lot going for it with only one real downer for us - the way the monoblock system works using an indoor unit, connected to the outdoor unit by water - not refrigerant, which is very large. I like the way they give you the depth of modulation and share all the stats around air temp / flow temp / COP.

[JamesPa]

14 hours ago, sharpener said:

 

I had a boiler installed in 2010, the installer (subcontractor to loft conversion ppl) had never heard of WC, I specified a Vokera bc it was the smallest I could find with WC but he had no idea how to wire it. I consulted Vokera technical who said to fit an external relay to inhibit the WC when HW calls for heat. Not a neat solution, they could easily have put a HW demand input on the pcb at no cost to themselves.

My (early 2000s era) Worcester Bosch gas boiler can cope with separate flow temperatures for CH and DHW, but only if you use their (add-on & overpriced) internal diverter valve.  It also does weather compensation with an add on (analog) module - which i don't have, is no longer obtainable and may not have been sold in the UK anyway.

 

A friend of mine has a very recent boiler from another (Dutch or German) company.  This has native weather compensation and also depends on the use of an internal, add-on, diverter valve if you want different flow temperatures for DHW vs CH, which obviously you do if using WC.  

 

My friend has shunned the over priced diverter valve and instead switches a resistor in/out of the line to the external temperature sensor, thus fooling the unit into thinking that the external temperature is very low when he heats hot water.

 

Is the Volkera the same I wonder?

Edited September 10 by JamesPa

[sharpener]

38 minutes ago, JamesPa said:

Is the Volkera the same I wonder?

 

Yes, I have fitted an external trimpot to get the WC right with the HW temp I want. It is not perfect bc adding external fixed resistors whether series or parallel will necessarily reduce the sensitivity to changes in the WC sensor resistance.

I don't think these workarounds should be necessary, as they are way beyond nearly all users and most installers too.

As upthread it would be sufficient for the mfr to add (i) an HW demand input and (ii) firmware which will store the HW temp setting if you adjust the knob while the demand is present and the WC curve otherwise. Knob is a s/w setting anyway, it does not directly define the h/w temperature. Not rocket science. Marginal manufacturing cost essentially zero.

[JamesPa]

34 minutes ago, sharpener said:

I don't think these workarounds should be necessary, as they are way beyond nearly all users and most installers too.

As upthread it would be sufficient for the mfr to add (i) an HW demand input and (ii) firmware which will store the HW temp setting if you adjust the knob while the demand is present and the WC curve otherwise. Knob is a s/w setting anyway, it does not directly define the h/w temperature. Not rocket science. Marginal manufacturing cost essentially zero.

Agreed.  My boiler actually has two flow temperature knobs, one for ch and the second for dhw.  The second is disabled if you don't have their internal diverter valve.  Why they couldn't have provided a connection to switch between the two flow temperatures if you have an external valve is anyone's guess.

[JohnMo]

1 minute ago, JamesPa said:

The second is disabled if you don't have their internal diverter valve.

Technology reduced for a backward UK market - suitably amplified by the OP plumber thinking he needs S or Y plan for a heat pump.

[marshian]

9 minutes ago, JohnMo said:

Technology reduced for a backward UK market - suitably amplified by the OP plumber thinking he needs S or Y plan for a heat pump.

Amen to that - general knowledge base is poor and the general view is the UK doesn't need or want the benefits of DHWP / X plan - it's S or Y plan and that's your choice...........

 

I my case I specified DHWP and "X plan" and I got a weather compensated S plan because the Gas engineer didn't know what X plan was - I should have got him to fit the boiler and commision it and done all the rest myself!!!