Controlling underfloor heating in passive house

[TerryE]

1 hour ago, dogman said:

Will the pump draw well enough through the mixer/blending valve if only partially open?

 

And just adding to what Nick says, in this case I will be circulating the water from the heater in the 23-28°C range and the blender TMV will be set at over 30, so the water will always be "too cold" and so the TMV will always be open.

[Nickfromwales]

The TMV then just becomes a failsafe device in case the Willis heater / its controller goes nuclear and tries to delivery heat to its infinity. 

So basically, you can't do away with the TMV even if you don't 'need' it . 

[TerryE]

The Willis has its own 60°C cut-out and I've also got a high level one.  Even so -- yes, you are right.  If the Wills and cut-out and my high level control logic all fail, then at least the TMV ensures that any consequences are above the slab and repairable.

[Calvinmiddle]

Still not sure why my plumber fitted the pump

on the buffer.....

maybe he didn't realise a NC value can take a few mins to open on the return side to complete the circuit to the buffer?

[dogman]

Thanks @Nickfromwalesand @TerryE 

 

That's what i needed from the boffin's,  a dummies guide to components without the added calculations.

 

[dogman]

On 15/03/2017 at 10:46, Nickfromwales said:

Buffer tank with a coil is best imo

Next simple thing. 

If you use a tank with coil (of any type) and wish to use the buffer tank to carry out DHW uplift aswell,

would the HP be connected to the volume and the cold main feed to your hot water system of choice be connected to the coil.

[Nickfromwales]

39 minutes ago, Calvinmiddle said:

Still not sure why my plumber fitted the pump

on the buffer.....

maybe he didn't realise a NC value can take a few mins to open on the return side to complete the circuit to the buffer?

Either that or he hadn't opened the TMV fully. 

As you will still have a water path through the pump I'd disconnect the electric to the pump and fire it up from cold. If you get heat flow after <10 mins or so you've got your answer. .  

[Nickfromwales]

3 hours ago, dogman said:

Next simple thing. 

If you use a tank with coil (of any type) and wish to use the buffer tank to carry out DHW uplift aswell,

would the HP be connected to the volume and the cold main feed to your hot water system of choice be connected to the coil.

Yes. That way you keep the potable ( drinking quality ) water completely separate. I would not use a coil on the ashp, but would instead feed the buffer 'volume' direct as that'll have the quickest recovery / transfer rates of heat from the HP to the buffer / TS. 

 

Edit to add : that brine ( HP water ) needs antifreeze so I'd recommend a stainless coil for DHW uplift. You don't want those two bodies of water ever mixing ☠️

[dogman]

@Nickfromwales

 

can you use an off the shelf indirect copper stainless steel cylinder or would you use one with a high efficiency coil

Edited March 16, 2017 by dogman

[Nickfromwales]

Telford are who I use primarily TBH. They'll make a cylinder bespoke but others have bought them elsewhere, so maybe ask in a separate thread as that'll be a subject of its own, ( so best not to bury it here  ). 

No real need for high efficiency ( aka high recovery ) coils with a low energy house as you just never need to inject that much heat in in any one go. More 'slow and steady' with a heat pump.

[Calvinmiddle]

3 hours ago, Nickfromwales said:

Either that or he hadn't opened the TMV fully. 

As you will still have a water path through the pump I'd disconnect the electric to the pump and fire it up from cold. If you get heat flow after <10 mins or so you've got your answer. .  

 

Experiment for the weekend, will report back

[Nickfromwales]

Just now, Calvinmiddle said:

 

Experiment for the weekend, will report back

Thanks. Will be good feedback. ?

[Calvinmiddle]

Hmm

Not sure I can do this experiment - as the pump in the first photo is wired into the timer that controls the pump that goes from buffer to manifold.  The pump on the manifold and also the NC value.

So no way to isolate the pump in the photo from the NC value which is what I would really need to do.

[Nickfromwales]

Just dewire the pump and put the cable ends into connector blocks ?

Or does that pump have a wireable plug that you can remove ? All you need to do is lift the live and just conn block it, don't even need to remove the wire tbh. . 

[Alex C]

I am at the stage of fitting the controls for heating of my passive and slab and as others have done I want to be able to circulate the water in it without heat input. Any suggestions as the best way to do this, My electrician has suggested using the loxone automation system and relays as it is already installed, but I would rather it was done using standard controls so anyone can fix it if there is a problem. Heating is via gas boiler. @JSHarris I was planning originally to run 2 zones off the 8 port manfold with 2 room stats. My plumber although good is very old school and has not been much help with suggesting ways to control this.

[Jeremy Harris]

I run ours as a single zone, with a single channel time switch/programmer controlling the power to the pump and to the two thermostats (one for heating, one for cooling).  The timer sets when water is circulating around the UFH loops, irrespective of thermostat settings.  The thermostats control whether heating or cooling is selected, setting the appropriate connections on the ASHP and to the valves.

 

It uses off-the-shelf parts, and the most likely control system parts to ever fail (timer, valves, relays and thermostats) are all off-the-shelf standard parts, that could be replaced quickly and fairly easily if there was ever a problem.

[ragg987]

I used a separate timer (Neostat) for the passive circulation and a UFH wiring centre (heatmiser UH4) to control the overall logic - very simple and no automation systems required. Schematic attached.

 

The Hitachi 3-way valve is used to open or close the supply of heated water from ASHP to UFH. When off, the circuit is closed, ASHP is off and the timer controls if pump needs to be on for passive circulation.

 

Edited April 26, 2017 by ragg987
clarify logic

[Guest Alphonsox]

I have unashamedly copied Jeremy's solution with the exception that I don't have cooling implemented. The slab is a single zone with the UFH circulation pump controlled by a time switch. A wireless thermostat opens a normally closed valve on the end of the manifold to allow hot water flow when the room cools down. This seems to be working well and is just about the simplest control system imaginable. Total cost of around £70.

 

[Alexphd1]

it sounds like a very simple solution !

Does anybody want to buy a dozen roomstats ?

Edited April 26, 2017 by Alexphd1

[jack]

Given how simple the control system will likely be, it wouldn't worry me that Loxone isn't an off the shelf controller.  You can explain how it all works to a plumber in three mins, especially if you document it properly with a system diagram.

 

Since you already have Loxone installed, and have the necessary relays free, presumably Loxone is also the cheapest option?  

[PeterW]

You can use the third timer on some of the newer controls - one for heating, one for DHW and one to control the circ pump

[IanR]

2 hours ago, Alex C said:

My electrician has suggested using the loxone automation system and relays as it is already installed, but I would rather it was done using standard controls so anyone can fix it if there is a problem.

 

I'm trying to change the least amount possible from a standard install, but to still allow Loxone to control UFH recirc. Here's what I have being installed at the moment (not yet proven)

 

 

I wish to exclude the buffer when I recirc so I've added a Normally Closed valve in between UFH pump and buffer plus a Normally Open valve between that and the return.

 

Loxone will ultimately control what the heating system is doing via Modbus comms into the heating controls, but in recirc mode, called by a delta between two slab temperature probes, Loxone will switch on the GP10 pump. If heat or cool is called then Loxone will power the NC & NO valves.

Edited April 26, 2017 by IanR

[Alex C]

Thanks for all the speedy responses. @jack Maybe i have been over concerned about using the loxone for control. All it will be doing is acting as a temp sensor and glorified timer. I always worry slightly though when you need to open an app or laptop to access basic things, like altering heating settings. I guess the reality is once it is set up to how we want it will never be changed again. I can't ever imagine wanting to turn on my heating when i'm on holiday or any other such home automation nonsense.

[Jeremy Harris]

12 minutes ago, Alex C said:

I always worry slightly though when you need to open an app or laptop to access basic things, like altering heating settings. I guess the reality is once it is set up to how we want it will never be changed again. I can't ever imagine wanting to turn on my heating when i'm on holiday or any other such home automation nonsense.

 

I think concern about apps controlling long-lived domestic equipment is extremely well justified.  The life cycle of IT kit in general is massively shorter that stuff in houses, and we regularly see items of hardware that are just a few years old lose all support.  Two examples, the gizmo my other half bought to transfer photos from her iPad to a USB stick lasted 6 months before an "update" made it into a useless paperweight, my scanner that stopped being supported two years after I bought it and so is similarly a paperweight, as there are no drivers for any newer software.

 

As another, commercial, example, my last work programme included building offices and labs for 900 members of staff.  When it was designed a "state of the art" Building Management System was installed, that included hundreds of sensors all over the building, central control of everything from climate to lighting etc.  This was all controlled by a relatively small server rack and a single terminal.  Within a year of the building being completed, Microsoft announced the demise of the underpinning operating system.  A year later the hardware was all made obsolete by the manufacturer, as they had upgraded in line with Microsoft changing the operating system.  Nothing was backwards compatible.  The choices were to spend the thick end of £100k on an all-new system (that would probably be obsolete again within 5 years) or take the slightly bizarre action of scouring eBay and buying up every spare for the two year old system we could find, to give us a working buffer stock of spare for another ten years or so.  We took the latter action, as there was no way that I was going to face the Public Accounts Committee and tell them that our state of the art, BREEEM Excellent rated, new flagship building was already obsolete...................

Edited April 26, 2017 by JSHarris

[jack]

These are real concerns Jeremy, I agree.  But Alex has already installed a home automation system.  In such a situation, it seems reasonable to me to use it, especially where the system involved is very well adapted to the type of application being discussed.

 

We use our HA system for lights, blinds and UFH control, as well as monitoring some temperatures.  I haven't bothered integrating it with the MVHR or ASHP, because the proprietary interfaces for those are ludicrously expensive (although I'll eventually end up controlling the MVHR speed setting by way of relays that close dry contacts).  

 

I've found myself very rarely having to access the app for Loxone, as most of the things I actually want to control day to day can be controlled by way of wall switches. The blinds are mostly automatic (all come down at dusk, some come up at 07:30, others - bedrooms, mainly - are closed automatically but opened manually by way of a wall switch).  The lights are all controlled by pushbuttons in a fairly similar way to ordinary lightswitches, although I've set it so that turning on certain lights in the daytime will result in a higher light output than turning them on at night.

 

I can check slab, air and DHW tank temps via the HA app, but this is mostly just because I'm interested, as none of those things are currently controllable via the app.

 

 

Also, even if the the HA system itself becomes obsolete or the company goes out of business, the way the house is wired means that any other system could be transplanted in with relative ease.  It's mostly just relays and simple programming, so not difficult to replicate in another system if ultimately required.  I hope to get 10 years out of the current system.  I have no idea what will be available then - with luck, HA will have become cheaper, easier and more secure by then.

 

I don't know whether I'd bother with HA if I were doing all this again, but it is definitely very convenient for things like automatic external blind control.