UVC Retrofit: Tundish D2 Discharge Pipe in a Passive House

[TerryE]

We've just bought an OSO SX250 UVC to replace or 2×SunAmp PV for the G3 plumber to fit sometime this next month. I have it sitting in situ in the utility room, though still unconnected, ATM.  (It is really a nice piece of kit:  I was initially planning to put a folding door cupboard in front of it but now that it is in situ, we agree that there is no point as its aesthetics are no worse than any other white goods unit.)  My plumber has done one quick site visit, but I am just getting my ducks in a row and trying to anticipate issues before we finalise his work plan.  

 

The main hassle is the tundish discharge pipe (D2) run because doing a new open external discharge would will be a total PITA because of (i) our MBC 300mm twinwall + ext stone skin, and (ii) not having an unsealed opening screwing up our airtightness.  I was wondering if anyone has used one of the new G3 compliant integral tundish + dry traps  (e.g. this Altechnic one).  This neat piece of kit kills quite a few issues such as maintaining airtightness, and being able to run 22mm copper D2 drain along a wall (which would allow us to snake behind a freezer) direct into Part G compliant branch.

 

@JohnMo, you posted on OSO's.  Do you or anyone else have a view?

 

Edited March 4 by TerryE

[SimonD]

I've used both Hotun and Macalpine self sealing tundishes, but not the Altechnic one. Your plumber should be on top of this as it's nothing unusual for an unvented installation.

[Nickfromwales]

On 04/03/2024 at 17:18, TerryE said:

We've just bought an OSO SX250 UVC to replace or 2×SunAmp PV for the G3 plumber to fit sometime this next month. I have it sitting in situ in the utility room, though still unconnected, ATM.  (It is really a nice piece of kit:  I was initially planning to put a folding door cupboard in front of it but now that it is in situ, we agree that there is no point as its aesthetics are no worse than any other white goods unit.)  My plumber has done one quick site visit, but I am just getting my ducks in a row and trying to anticipate issues before we finalise his work plan.  

 

The main hassle is the tundish discharge pipe (D2) run because doing a new open external discharge would will be a total PITA because of (i) our MBC 300mm twinwall + ext stone skin, and (ii) not having an unsealed opening screwing up our airtightness.  I was wondering if anyone has used one of the new G3 compliant integral tundish + dry traps  (e.g. this Altechnic one).  This neat piece of kit kills quite a few issues such as maintaining airtightness, and being able to run 22mm copper D2 drain along a wall (which would allow us to snake behind a freezer) direct into Part G compliant branch.

 

@JohnMo, you posted on OSO's.  Do you or anyone else have a view?

 

I use the McApline on every install, and all projects are airtight etc. These just go to the soil stack wherever that connection is practically made. 
The G3 regs state the maximum length of the D2, including reductions for 90° bends etc, so you may have to beef that up to 28mm   

[TerryE]

4 hours ago, Nickfromwales said:

The G3 regs state the maximum length of the D2, including reductions for 90° bends etc

 

Thanks Nick. The direct distance UVC to stack is ~3½ m so even with the elbow reductions we are well under the 9m limit for 22mm.

[Duncan62]

On 04/03/2024 at 17:18, TerryE said:

We've just bought an OSO SX250 UVC

 

 

Who did you buy it from please?

I'm after a 300L one this year.

[JanetE]

We got our OSO cylinder from a company called Electrical Deals Direct, based in Weston-super-Mare.  Keen price and excellent service with quick delivery.  We can recommend them. 

Edited March 11 by JanetE
Spelling error

[Nickfromwales]

11 hours ago, Duncan62 said:

 

Who did you buy it from please?

I'm after a 300L one this year.

If it is a generic UVC you are after, then you can also try Trevor at cylinders2go, and mention the forum.

[Duncan62]

58 minutes ago, Nickfromwales said:

If it is a generic UVC you are after, then you can also try Trevor at cylinders2go, and mention the forum.

Thank you, should have said specifically the OSO tank, as it has very low heat loss.

[Nickfromwales]

44 minutes ago, Duncan62 said:

Thank you, should have said specifically the OSO tank, as it has very low heat loss.

Get the stats from Telford too. "Go compare" lol.

 

[Duncan62]

11 hours ago, Nickfromwales said:

Get the stats from Telford too. "Go compare" lol.

 

Ok.

 

They loose double the amount of heat compared to the OSO, on a 300L UVC, 2.32kwh/24hrs vs 1.18kwh/24hrs

 

Telford: https://www.tdlonline.co.uk/Heating/Hot-Water-Cylinders/Telford-Stainless-Cylinders/Telford-Tempest-Cylinders-Heat-Pump-Coil/6134-/Telford-Tempest-300-Litre-with-Heat-Pump-Coil-33sqm-TSMI300HP

 

OSO: https://osohotwater.co.uk/product/delta-coil-dcpp/

[TerryE]

On 12/03/2024 at 08:18, Duncan62 said:

They lose double the amount of heat compared to the OSO

 

The wonders as formed vacuum panel insulation. 🙂

[JohnMo]

On 12/03/2024 at 08:18, Duncan62 said:

They loose double the amount of heat compared to the OSO, on a 300L UVC, 2.32kwh/24hrs vs 1.18kwh/24hrs

The heat loss test basically heats cylinder to 65 degs in a 20 deg room and maintains that temperature for 24 hrs and measures how much energy is required to keep it at 65 degs.

 

But storing water at 45 to 50 your losses become really low. Reducing by around 50% for both cylinders. I would think the biggest difference to cylinder heat loss, is the piping install and insulation which is never mentioned or included in the heat loss figure. 

 

Store at a lower temp and don't worry about it. But some perspective the oso delta geo coil is £1800, my slim line cylinder was £1000. It would take 40 years of savings to make up the cost difference.

[jack]

18 minutes ago, JohnMo said:

Store at a lower temp and don't worry about it.

 

I think we ought to be encouraging larger tanks.

 

They store the same amount of energy at a lower temperature (suits ASHPs) in the colder months, and allow greater usage of diverted PV power when the sun is shining.

[Nickfromwales]

11 hours ago, JohnMo said:

The heat loss test basically heats cylinder to 65 degs in a 20 deg room and maintains that temperature for 24 hrs and measures how much energy is required to keep it at 65 degs.

 

But storing water at 45 to 50 your losses become really low. Reducing by around 50% for both cylinders. I would think the biggest difference to cylinder heat loss, is the piping install and insulation which is never mentioned or included in the heat loss figure. 

 

Store at a lower temp and don't worry about it. But some perspective the oso delta geo coil is £1800, my slim line cylinder was £1000. It would take 40 years of savings to make up the cost difference.

Took the words right off of my keyboard lol. Damn right.

I'd rather put the other £800 into everything else.

[TerryE]

In our case  the UVC is free-standing in a utility room, which is basically a corridor from the hall to the back door with sink, worktops and whitegoods along one side.  The OSO UVC fits in a gap behind the hall door, and is in open view.   Because the room is only about 8m² area inside a passive house, a conventional UVC would be unsightly and would turn it into a hot room.  As for the extra £400 or so, IMO this is a small price to pay to keep Jan happy and maintain harmony in the household.

 

I am fitting a couple of digital thermometers on the tank, so I can use these to tune the Immersion timing.

 

Edited March 15 by TerryE

[WisteriaMews]

@TerryE @JanetE I'm looking to specify the same tank in my new passive self build, but have been struggling to find out many specifics about the controls.

 

Ideally I think I'd like to:

1. Heat to full overnight on off peak electricity - it sounds like it has timers so this should be possible.

 

2. If the tank falls below a certain level boost it so there is enough hot water for evening showers / so we don't run out etc... - I haven't been able to find anything on a 'smart' feature like this being possible.

 

Are you able to share your experience with the tank controls.

 

Thanks.

[ProDave]

On 15/03/2024 at 02:43, TerryE said:

Because the room is only about 8m² area inside a passive house, a conventional UVC would be unsightly and would turn it into a hot room.

We have a Telford 300 litre heat pump UVC.  It was only last year I built the airing cupboard around it (it's in the corner of the small bedroom to give optimum short hot pipe runs) so now it is in an enclosed small space.

 

I had expected that airing cupboard to be a real hot house, but it is only a few degrees hotter than the room it is partitioned off from.  That is a testament to how little heat it loses, mostly down to all the pipework being well lagged as already mentioned, and storing water at 48 degrees.

[ProDave]

On 04/03/2024 at 17:18, TerryE said:

We've just bought an OSO SX250 UVC to replace or 2×SunAmp PV

What's the issue with the Sun amps?

[Duncan62]

On 04/03/2024 at 17:18, TerryE said:

We've just bought an OSO SX250 UVC 

 

Where did you pick one up please?

[TerryE]

@ProDave, in a nutshell, our decision to replace the SunAmps was because of the poor reliability of their engineering implementation: the circuit boards broke basic layout design guidelines, e.g. lack of 240V isolation and inadequate track sizing for 3kW power routing, so they had an MTBF of maybe 2 years; all of the pump and control plumbing was hidden inside a pretty steel case, which looks sexy but makes maintenance and repair a total dog.  Yes, the concept of a PCM thermal store for DHW has great potential, but not this model and company.

 

@Duncan62, Jan is our procurement specialist; she found a supplier online, which had the model we wanted in stock and could deliver it in a week.  Seek and ye shall find.

 

@WisteriaMews,  We have an electric-only passive-class house.  All of our white goods use timer-controllable cold-fill in-device heated water, so our HW use is pretty low: primarily showers for three adults and occasional shared baths for the 2 OAPs (mostly in the winter). Our OSO model is double immersion heated only, which makes sense for our use.  I need to do I full blog post on this, but my CH control system uses 4×Finder contactors driving the 2 OSO UVC Immersions, my UFH pump and a 3kW heater that heats the UFH.

 

I use  Home Assistant to do the user interface and graphics for my Home Automation, but in terms of CH and HW control I have a custom NodeRED application (about 900 lines of Javascript that I wrote) to control a 4-relay Tasmota module via MQTT, and this in turn outputs 24V control signals to drive the contactors.  I buy my electricity using an Octopus Agile Tariff.  This has an API which published its day-ahead half-hourly prices at around 5PM starting midnight C.E.T.  In essence, at 11PM each night, this app schedules the daily CH and HW heating for the next 24 hrs to use the cheapest half-hour slots.

 

In terms of  HW and heating the OSO, I have installed top and bottom digital thermometers to monitor the tank temp.  The app uses these 2 tank temps to estimate the total kWh needed to bring the tank up to 50°C and it uses the day-ahead prices to schedules the cheapest time slots to heat the tank.  (If the top temp falls below a preset, it also stuffs in a ½hr top-up regardless of price, but this happens so rarely that this isn't a significant cost premium for always having HW.)  The OSO has a parasitic loss of just over 1 kWh / day, plus replenishing used water, which varies but is typically equates to another 2-3 kWh at most except during the winter bath season.  The kWh price for this last couple of weeks has been negative on 4 days , small pence on another 4 and only peaking at 14½p on the stiller overcast days, so the cost of of our water use runs at under 50p / day on average.  We tend to have our big bath days when Octopus will pay us to do this or it only costs pence.

 

I've been coding for over 50 years so the Javascript bit is easy for me, but I understand that those who aren't so IT literate will have a lot fewer options.  I believe the like of Octopus and OVO are exploring some Smart Control options, but these aren't yet prime time.

Edited September 5 by TerryE

[jack]

12 hours ago, TerryE said:

I've been coding for over 50 years so the Javascript bit is easy for me, but I understand that those who aren't so IT literate will have a lot fewer options.  I believe the like of Octopus and OVO are exploring some Smart Control options, but these aren't yet prime time.

 

For anyone using Loxone, there's a module that integrates with ToU tariffs, particularly Octopus Agile: https://www.loxone.com/enen/kb/spot-price-optimizer-uk/

 

For example, if you predict that you need four hours of heating a day when it's cold, you can tell it to turn the heating on during the four cheapest hours. Given the flexibility of Loxone programming, I'm sure you can probably do a hell of lot more with it as well (e.g., automically turn things on when the energy price is negative).

 

It sounds like it's a bit complicated to set up initially, and not quite perfect in terms of knowing actual prices, but hopefully they'll be able to get full integration working @Dan F:

 

[WisteriaMews]

@TerryE thank you for the detailed reply. I'm not as IT savvy so the above is probably a bit advanced for me! 🙂

 

Might be a silly question, but how.did you install the top and bottom thermometers? I'm assuming they are on the outside of the tank? Did you try to get round the insulation to install them on the metal skin of the tank?

 

It sounds like you only use a top temperature sensor to drive the boost if needed? Being able to have a boost is my main concern, so I might be able to do something simpler than your setup. (I'm planning to be on Go / Flux rather than Agile so will have a set block of off peak that I can just use a timer for.)

[TerryE]

@WisteriaMews, sorry I am in Greece ATM, and so not checking the forum daily. 

 

The OSO UVC has an double skin: inner steel pressure vessel and our plastic or powder coated aluminium with vacuum panel insulation between.  The two immersions are installed in small access panels with the wiring terminals, thermostatic switches  etc.  There is an internal duct channel for the 3kW flex cabling running from the bottom to up the two access panels.  I used a couple of waterproof ds18b20 digital thermostats to measure temperatures.  Look them up on eBay etc.   The "waterproof" bit isn't important, but they are encapsulated in a ~8mm dia aluminum can that can be thermal-taped directly to the steel cylinder with a bit of foil+mineral wool insulation on top; you can get a get a range of lead lengths but 1½ or 2m  is enough to take it down to the bottom channel of the cylinder, and thin enough to be run alongside the flex in the internal cabling duct.  These thermometers are wired into a small IoT board, a Wemos D1 Mini which in a small ABS box about 25×40×50mm IIRC and powered using a USB lead; This ESP8266-based module  uses ESPhome firmware to talk back to my home automation system over local Wifi.

 

I use the Node-RED javascript code to track temperatures, do the heating calcs, and send the MQTT commands to power on and off the power to the two immersions. Here is a screen grab from my Home Automation system for the last 24 hours.  You can see that my son had a bath or long shower at 5PM, and it scheduled top up at 00:30, 04:30 and 09:30 to bring the UNC to target 50°C because of the cheap spply pricing in those slots.   (The price actually went negative in two of these slots so I actually got paid to heat the water.) 

 

The ~ 4°C cooling / day is the parasitic heat loss from the UVC which is very small compared to conventional cylinders or thermal stores.