Why UFH?

[joe90]

1 hour ago, Nickfromwales said:

For the amount of heat you’d need from them, if used in conjunction with wet UFH in the main slab, I’d stick to the sheer simplicity of electric towel rads + electric UFH. 

 

This is what I did and it works great, didn’t want to run UFH pipes upstairs, and as @JSHarris says above about temp etc. KISS ?

[ProDave]

You definitely won't get a lot of heat from a towel radiator fed with UFH temperature water in a modern well insulated house.  If you put your hand on the UFH flow from the ASHP it barely feels tepid, that's how your towel rail will feel.

 

Even the floor does not feel "warm" more a case of it not feeling cold.

[Robert Clark]

11 minutes ago, ProDave said:

You definitely won't get a lot of heat from a towel radiator fed with UFH temperature water in a modern well insulated house.  If you put your hand on the UFH flow from the ASHP it barely feels tepid, that's how your towel rail will feel.

 

Even the floor does not feel "warm" more a case of it not feeling cold.

I was wondering if the towel rails cold be fed from a high temp circuit like the hot water tank

[ProDave]

1 minute ago, Robert Clark said:

I was wondering if the towel rails cold be fed from a high temp circuit like the hot water tank

I guess if you have a hot water tank that is ported for hot water circulation (our Telford UVC is) then you could pipe hot water from the DHW tank through the towel rail.  We run our DHW tank at 48 degrees so that would be okay for the towel rail.  But someone will come along in a minute and tell us why that would not be a good idea.  Rusty brown hot water?  Might need a Plate Heat Exchanger to prevent that.

 

It sounds an awful complication to avoid just having an electric towel rail.

[SteamyTea]

4 minutes ago, ProDave said:

It sounds an awful complication to avoid just having an electric towel rail.

Yes

KISS

again

[TerryE]

We've got one towel rail in our master bedroom ensuite and TBH we don't use it.   It is really hard to really understand what it is like living in a PH unless you do so, because the experience is so counter-intuitive to all of your pre-PH experience.  The whole fabric of the house  is within ±½°C or so of the mean, and even if you are topping the heat up overnight there is still maybe about ±½°C ripple on this at most.  There aren't cold spots; there aren't cold periods. 

 

I've got UFH in my slab, and nothing else (other than that towel rail).  My HA system does some sums each night and calculates the kWh input needed for the following day as a simple function of the average forecast temp for the following day and the delta between the target set point (we have ours as 22.4°C) and the overage over the day.  So let's say it calculates this as 12 kWh, then the Willis is turned on from 03:00-07:00 so that we use E7.  That's it.

 

I do have a few tweak that I want to do:  when we have visitors then we should really offset the heat demand for the extra heat from their bodies, but we don't so the air temperature will heat up a degree or so because of the extra walking radiators, but this rapidly goes back to normal when thy leave as the fabric temperature doesn't really move.

 

I also "cheat" by having a small oil radiator on a Sonoff timer in Dec/Jan when I need more than 7 × 3 kWh  heat, so I use the rad to add extra space head during the E7 window.

 

It is all really simple: if your house loses X kWr/day at your target environment temperature and with the current outside temperatures, then if you put X kWh heat into the house, (and it doesn't really matter too much how you do this),  the house will stay within a small tramline of that target.

 

As the others have said my whole system for my reasonably large 4/5 bedroom house cost ~£4K to install, and that included the UFH.  I have no maintenance costs.  My total energy costs for the warm 7 months are less that the annual maintenance on the Gas CH system in my last house.

Edited October 27, 2019 by TerryE

[Robert Clark]

1 hour ago, TerryE said:

We've got one towel rail in our master bedroom ensuite and TBH we don't use it.   It is really hard to really understand what it is like living in a PH unless you do so, because the experience is so counter-intuitive to all of your pre-PH experience.  The whole fabric of the house  is within ±½°C or so of the mean, and even if you are topping the heat up overnight there is still maybe about ±½°C ripple on this at most.  There aren't cold spots; there aren't cold periods. 

 

I've got UFH in my slab, and nothing else (other than that towel rail).  My HA system does some sums each night and calculates the kWh input needed for the following day as a simple function of the average forecast temp for the following day and the delta between the target set point (we have ours as 22.4°C) and the overage over the day.  So let's say it calculates this as 12 kWh, then the Willis is turned on from 03:00-07:00 so that we use E7.  That's it.

 

I do have a few tweak that I want to do:  when we have visitors then we should really offset the heat demand for the extra heat from their bodies, but we don't so the air temperature will heat up a degree or so because of the extra walking radiators, but this rapidly goes back to normal when thy leave as the fabric temperature doesn't really move.

 

I also "cheat" by having a small oil radiator on a Sonoff timer in Dec/Jan when I need more than 7 × 3 kWh  heat, so I use the rad to add extra space head during the E7 window.

 

It is all really simple: if your house loses X kWr/day at your target environment temperature and with the current outside temperatures, then if you put X kWh heat into the house, (and it doesn't really matter too much how you do this),  the house will stay within a small tramline of that target.

 

As the others have said my whole system for my reasonably large 4/5 bedroom house cost ~£4K to install, and that included the UFH.  I have no maintenance costs.  My total energy costs for the warm 7 months are less that the annual maintenance on the Gas CH system in my last house.

what bit of kit calculates how long the Willis heater will run for?

[SteamyTea]

1 hour ago, TerryE said:

My HA system does some sums each night and calculates the kWh input needed for the following day as a simple function of the average forecast temp for the following day

I have a number of questions about this.

Do you fancy starting something in Boffins Corner?

[TerryE]

2 hours ago, Robert Clark said:

what bit of kit calculates how long the Willis heater will run for?

 

No kit at all.  I have a couple of DS18B20s in  the wall fabric to get the average house and the external temperature forecast is a NodeRED HTTP request to datapoint.metoffice.gov.uk.  This goes into a NodeRED function node (~60 lines of Javascript).  The estimator has two linear terms with coefficients starting on my modelling of the house performance but then adjusted base on a fit of historic data.

 

My HA system is an RPi + SSD, total cost ~£70.  All the data logging and relay control is done through ESP8266s, total cost maybe £20.  The most expensive bit were the 16A SSRs used to switch the Willis and SunAmps at around £45 each IIRC.

 

2 hours ago, SteamyTea said:

I have a number of questions about this.

Do you fancy starting something in Boffins Corner?

 

Sure, but why don't you start the ball rolling just @ me so I pick it up ?

 

Edited October 27, 2019 by TerryE

[TerryE]

One of these days I will have time to write all of this up but my major post-build hobby is acting as the lead developer for an IoT firmware: I am upgrading the firmware to a Lua 5.3 version and fighting getting a £2 chip to run 15K lines of dense test vectors ?

[scottishjohn]

7 minutes ago, TerryE said:

One of these days I will have time to write all of this up but my major post-build hobby is acting as the lead developer for an IoT firmware: I am upgrading the firmware to a Lua 5.3 version and fighting getting a £2 chip to run 15K lines of dense test vectors ?

sounds like if it was  in a box it could a wee biusness for you

[TerryE]

On 25/10/2019 at 10:42, Robert Clark said:

In a Passivhaus where heating is seldom required, why would you use UFH which is slow to heat up when slimline electric heaters would deliver heat quickly and maybe more controllably ?

 

Rob, can I just emphasise a fundamental characteristic of at least our PH.  Nothing happens quickly.  If you stopped heating it in winter it would only drop about 1°C/day at most and heating it up again is pretty sluggish as well, so its just far easier to keep the whole house at the same temperature all of the time. 

 

The one caveat here is if you've allowed your architect to persuade you to have "acres of glass" especially south facing, because a serious dose of solar gain can turn a PH into a greenhouse in hours.

 

The other thing is the lack of zones controls, radiators on various walls etc.  The rooms are simple and clean and the walls are for hanging pictures, bookcases and putting furniture against.  

 

[joe90]

I agree with all said above. Ours is not quite passive (but sheds loads better than most builds!), we were warned about overheating because of our large south facing conservatory and bi folds into kitchen and lounge. Yes, in the (brief) summer it got a bit warm but no hotter than the south of France, so saved me paying for a holiday there!. Today the kitchen got down to 19’ first thing in the morning (had a ground frost) and the heating kicked in for a short while fir the first time this year, HOWEVER, lovely sunny day and kitchen and lounge quickly up to 20’ because of the solar gain, quicker that the UFH could raise that temp.!!! Actively thinking of going E7 to warm up the slab and DHW tank overnight.

 

P.S. Note to self, get a room stat with smaller hysteresis!

Edited October 27, 2019 by joe90

[PeterW]

6 hours ago, TerryE said:

If you stopped heating it in winter it would only drop about 1°C/day at most and heating it up again is pretty sluggish as well, so its just far easier to keep the whole house at the same temperature all of the time. 

So - interesting you say that..!!

 

Thermostat currently set at 18.5c, and heating was running on Monday. Been in today and thermostat says 15.5c as the zone valve motor has failed - temperature up here hasn’t been above 13c for most of the week so reckon that’s about a 0.5c loss per day. 
 

The flip side is that just putting the ASHP on for 2 hours only gained me 1c, will leave it to do its thing tonight on E7 and see what it is doing in the morning. 

[TerryE]

@PeterW be careful that you don't repeat what JSH did once - - which was to crank up the heating to try to get back to setpoint quickly.  If you do that then you'll get there reasonably quickly; and the temperature will the over shoot, and then oscillate as the slab vs the rest of the fabric get back to equilibrium.  IIRC Jeremy overshot to something like 26°C. 

[Nickfromwales]

13 hours ago, TerryE said:

The most expensive bit were the 16A SSRs used to switch the Willis and SunAmps at around £45 each IIRC.

Do you have a link to these please, and did you have to fit a heat sink to them? 

[TerryE]

@Nickfromwales I used the Crydom CKR range  which is supplied here by RS Components with other options.  These have an in-built heat sink and are Din mount so go well into a simple steel enclosure.  The nice thing about these is that they include an opto-isolated input that you can drive directly with a 5V 15mA [TTL] input.  Some of the Arduino GPIOs can drive this, but devices like the RPi and ESPs use 3.3V logic.  I use a MCP2008A 3.3V I2C to 8-port 5V driver IC to drive the Crydom iputs,, but another option is to use something like a SparkFun Logic Level Converter which surface mounts the MOSFET drivers to do this magic and costs a few £.

 

The advantage of using an RPi directly is that you can use something like NodeRED or one of the HA products to do all of the nasty S/W stuff.  Either contact me offline or raise a Boffin's topic and poke me if you want to go into more detail.

Edited October 28, 2019 by TerryE

[Jeremy Harris]

9 hours ago, TerryE said:

@PeterW be careful that you don't repeat what JSH did once - - which was to crank up the heating to try to get back to setpoint quickly.  If you do that then you'll get there reasonably quickly; and the temperature will the over shoot, and then oscillate as the slab vs the rest of the fabric get back to equilibrium.  IIRC Jeremy overshot to something like 26°C. 

 

 

I did indeed do exactly this.  The house took days to cool down.  It's really important to not put too much heat into the slab too quickly, I've found, to prevent overshoot.

[Nickfromwales]

7 minutes ago, JSHarris said:

 

 

I did indeed do exactly this.  The house took days to cool down.  It's really important to not put too much heat into the slab too quickly, I've found, to prevent overshoot.

I turn things up roughly 0.5^o per day, allowing the full 24hrs for things to acclimatise at their own pace. Takes a good week or so to get things to 'simmer down'.

Having the Ivar type blending set, a-la @JSHarris's type of set, is of huge importance as if you try to do this type of heating management with a normal thermo-mechanical type of blender ( aka TMV ) you''ll never reliably get down to a flow temp accurate enough to stop the above-mentioned overshoot. The room stat ( correct choice of ) is of equal importance.

If you don't get those two elements right you'll not stand a chance, but if you get it right the curve for the heating hysteresis will be as close to a flat line ( as possible ) eg a near equilibrium as far as achieving a comfortable thermal constant. 

PH is nuts, and very difficult to convey to those who have had no direct experience of 'it'. With a heated slab and the house at equilibrium you can open all the door and windows for 10 minutes when it's -5 outside, blow all the heat out of the house until you're freezing your knackers off, and then just shut the doors and windows back up again. Within 3-5 minutes the house is back to how it was. 

For those who don't want to fit UFH, in conjunction with a decent slab, good luck with that!! 

[Nickfromwales]

6 hours ago, TerryE said:

....poke me if you want to go into more detail.....

....sorry Terry, you're not my type  

 

Just a heads up on how a simple man like myself would switch one of these on / off from a 230v signal would help. I assume the 230v would fire the coil in a zero volt relay and I'd have to generate the 5v from an 3rd party adaptor / transformer and send that through the zero-volt side of the relay?

Simple on / off operation will suffice, mainly because I try and set things up so some poor fool would be able to reasonably quickly identify what's been done and how it works ( in the event of a breakdown and I'm not of this world anymore ) for fault-finding / ongoing maintenance & repair by A.N. Other.

 

I strayed into the Boffins corner once, but was chased back into the woods by a headless horse-man. 

[dpmiller]

SSRs are also available with mains control, if you require, Nick.

[joe90]

I,m with @Nickfromwales, KISS every time. Less to go wrong!.

[Pete]

1 hour ago, joe90 said:

I,m with @Nickfromwales, KISS every time. Less to go wrong!.

Sheepishly asking what does KISS refer to?

[Cpd]

3 minutes ago, Pete said:

Sheepishly asking what does KISS refer to?

KEEP
IT

SIMPLE

STUPID 

 

[Pete]

8 minutes ago, Cpd said:

KEEP
IT

SIMPLE

STUPID 

 

LOL, should have known, sorry will sit in the naughty corner with @AnonymousBosch