UFH mixing valve at low temps

[PeterW]

38 minutes ago, ProDave said:

Every blender I have seen has 4 ports and does not have a removable actuator with an M30 thread.  So I am now at a complete loss to know where you would put one of these Salus peoportional actuators.

 

The Wunda ones have two different types - one that does the “standard” 3 port blend (Return, Hot feed, output) and one that has a proportional valve like a rad valve with a remote sensor in a pocket in the top rail. 

 

48 minutes ago, Benjseb said:

the actuators are simply flow rate of the return feed. Sealed loop so can only co tell flow, not temp?

 

i guess it controls delta T by adjusting the flow rate 

 

Correct. It is using the delta change between water/concrete/air which is the rate of heating and applying it to the flow. A cooler room will absorb heat at a faster rate therefore it allows a higher flow rate as the return temp is cooler than a smaller loop or warmer room that is returning water at a faster rate and potentially has a lower heat transfer. 

[PeterW]

19 minutes ago, ProDave said:

Ah, so this will only work on some manifolds.

 

Here is mine (before being piped and wired)

 

 

The blending valve does not have a removable head, so I could not replace it with the Salus unit.

 

You would replace the 5 white heads at the bottom with the Salus heads - that would control the delta T by flow rate and you just open the flow valves up to full. 

[dpmiller]

but regardless of differental across each loop surely you're still at the whim of the TMV to set the flow supply temp.

 

I've specced two manifolds for ours- one for towel rails and rads with a Reliance mixer like @ProDave has,  bit the UFH looms utilise one with a capillary sensed blender (and bypass circuit) like @JSHarris shows. It's got a low temp head on too,  many capillary heads don't go down low enough for UFH purposes.

[Jeremy Harris]

57 minutes ago, dpmiller said:

but regardless of differental across each loop surely you're still at the whim of the TMV to set the flow supply temp.

 

I've specced two manifolds for ours- one for towel rails and rads with a Reliance mixer like @ProDave has,  bit the UFH looms utilise one with a capillary sensed blender (and bypass circuit) like @JSHarris shows. It's got a low temp head on too,  many capillary heads don't go down low enough for UFH purposes.

 

 

Yes, but that is no longer critical in determining how the system responds, as the Salus actuators do all the fine control.  The incoming flow temperature can therefore vary over a wider range without having much impact on response.  Prior to fitting these actuators our system would sometimes behave itself, with the flow running at around the 25° to 26°C that it was set too, but sometimes it would jump up to 30°C or more, due to variations around the set temperature within the thermostatic valve.  Now it doesn't really matter if the thermostatic valve doesn't run down at around the 25° to 26°C point needed for accurate control, as the system works just fine with that set to ~30°C and the Salus actuators making the fine adjustments.

 

I can't see why this wouldn't work with any sort of mixer valve, as all that matters is that the flow temperature is in the right ball park.  A degree or two flow temperature variation from the thermostatic valve natural variation at low settings no longer seems to have any impact on how the system behaves.

[Ed Davies]

So, could you dispense with the mixing valve and rely on the heat pump's temperature setting to control the flow manifold's temperature? Advantages would be avoiding the cost and potential failure of the mixing valve and, more significantly, allowing the HP to run at a lower temperature as mixing valves need at least a bit of a temperature drop? Or would that require too narrow a temperature range on the buffer tank making that pointless or large?

[Jeremy Harris]

4 minutes ago, Ed Davies said:

So, could you dispense with the mixing valve and rely on the heat pump's temperature setting to control the flow manifold's temperature? Advantages would be avoiding the cost and potential failure of the mixing valve and, more significantly, allowing the HP to run at a lower temperature as mixing valves need at least a bit of a temperature drop? Or would that require too narrow a temperature range on the buffer tank making that pointless or large?

 

 

I guess you could do that.  I run our ASHP at 40°C, as, by experiment, I've found that it never seems to run a defrost cycle when run at that temperature, but i could lower it and do away with the thermostatic valve.  The buffer would have less effect, but I'm not sure that would be that significant, as at the moment it can run the heating for around 3 hours at a fairly typical 400 W of heating demand, which is much longer than is really needed just to stop the ASHP short cycling.

[ProDave]

27 minutes ago, Ed Davies said:

So, could you dispense with the mixing valve and rely on the heat pump's temperature setting to control the flow manifold's temperature? Advantages would be avoiding the cost and potential failure of the mixing valve and, more significantly, allowing the HP to run at a lower temperature as mixing valves need at least a bit of a temperature drop? Or would that require too narrow a temperature range on the buffer tank making that pointless or large?

That is what I do with mine.  One of the user parameters is "water leaving temperature" which has two settings, one for DHW and one for space heating.

 

I still have the blending valve in circuit, set to it's lowest setting.  That protects the UFH when the HP switches from DHW mode to heating mode, from a slug of 55 degree water still in the pipes that would otherwise go straight into the UFH loops if the blending valve was not there.

[Ed Davies]

@JSHarris what temperature range does your buffer operate over? Dropping the range to, say, a third of whatever that is would mean running the HP hourly which seems reasonable to me.

 

@ProDave do I remember correctly that you don't have a buffer tank? Does your HP modulate down far enough to be able to run continuously?

[Jeremy Harris]

3 minutes ago, Ed Davies said:

@JSHarris what temperature range does your buffer operate over? Dropping the range to, say, a third of whatever that is would mean running the HP hourly which seems reasonable to me.

 

 

Typically about 15°C or so, as the flow to the UFH rarely needs to be higher than about 25°C.  Dropping the ASHP to 30°C would work fine, I'm sure, and still give about an hour of buffering in normal winter conditions.

[Ed Davies]

We need 1 kWh, or even a bit less, of PCM28, don't we?

[Jeremy Harris]

5 minutes ago, Ed Davies said:

We need 1 kWh, or even a bit less, of PCM28, don't we?

 

 

I believe that the other PCM that Sunamp developed was PCM 34, but yes, something around 28°C phase transition temperature would seem to be about right for charging with an ASHP.  I have a feeling that some paraffin waxes might be around that sort of temperature, but their volumetric storage density isn't that great, IIRC.

[Ed Davies]

1 hour ago, JSHarris said:

I have a feeling that some paraffin waxes might be around that sort of temperature, but their volumetric storage density isn't that great, IIRC.

 

Yes, here are some: https://www.rubitherm.eu/en/index.php/productcategory/organische-pcm-rt

 

RT28HC is 250 kJ/kg so would need 14.4 kg to store 1 kWh (volume about 18.7 L when melted). Bit more than I had in mind. Prices varied from 4.4 to 5.7 €/kg when I enquired in 2005. Also flammable.

[Nickfromwales]

@Benjseb

@dpmiller

This is a bit confusion here about what actuators go where. 

@Benjseb you need to bin the TMV you have as it is “a bit shit” as you say at these low flow / temps. 

I fit Ivar blending sets which work reliably down to 20 degrees at full flow potential. Utterly seem-less in operation and accurate as hell. 

You can fit the Salus heads onto each individual port and the open the flow regulator ( the bit that shows L/P/M flow rate ) fully as the Salus gave two flying leads ( thermo capillary ) which tell the actuator to open 100% ( until return is coming back hot ) and then to self regulate the L/P/M flow rate to that individual loop. That means short loops cannot bypass and cause issues with bigger loops being starved. 

You can then, if required, fit a single Salus actuator onto the blending valve instead of the supplied manual one. 

Clear as mud?

[Benjseb]

Yes all clear

 

at £200 to replace the actuators though I am wondering if it’s worth the expense. Our loops are all about the same length so not sure if we will get that much benefit

[Jeremy Harris]

14 minutes ago, Benjseb said:

Yes all clear

 

at £200 to replace the actuators though I am wondering if it’s worth the expense. Our loops are all about the same length so not sure if we will get that much benefit

 

Yes, they do add a bit of additional cost, but they are worth it, I think.  Out of interest, did you shop around for prices, as I found there was a very wide variation in price.  IIRC, I paid around £30, inc VAT, for ours, but some places were selling them for around £50, which was ludicrous.

[Dan F]

On 06/10/2019 at 17:28, Jeremy Harris said:

One fix is to just bin the mixing valve altogether and use the Salus differential temperature controlled actuators:https://salus-controls.com/uk/product/thb23030/.  I'm using one and find it very good at maintaining a steady temperature across manifolds.  These actuators also open and close a fair bit faster than the hot wax ones, which can be useful.  They maintain a 4°C temperature differential between UFH flow and return if the highest sensed temperature is below 30°C and a 7°C differential if the highest temperature is above 30°C.  I have ours sensing the flow and return temperatures on the UFH loops.

 

How do these Salus actuators behave when you run your UFH in cooling model?  Given when cooling you want your flow temp to be cooler than return temp..

[Jeremy Harris]

19 minutes ago, Dan Feist said:

 

How do these Salus actuators behave when you run your UFH in cooling model?  Given when cooling you want your flow temp to be cooler than return temp..

 

 

Luckily they work in exactly the same way in cooling mode as they do in heating mode, as they don't care which was around the sensors are placed.  In cooling mode they maintain a 4 deg C differential between flow and return, but the other way around.  Typically we'll get around 13 deg C flow and 17 deg C return, for a floor surface temperature of maybe 18 deg C.

[JFDIY]

21 minutes ago, Jeremy Harris said:

 

 

Luckily they work in exactly the same way in cooling mode as they do in heating mode, as they don't care which was around the sensors are placed.  In cooling mode they maintain a 4 deg C differential between flow and return, but the other way around.  Typically we'll get around 13 deg C flow and 17 deg C return, for a floor surface temperature of maybe 18 deg C.

 

So in cooling mode is the direction of water flow reversed?

 

So the cool side of manifold is still the same and vice versa? Otherwise won't the actuator sense the temperature differential back to front so to speak and then just open the actuator fully in the hunt to achieve the 4degrees but never get it and in effect just be wide open

[Jeremy Harris]

Just now, JFDIY said:

 

So in cooling mode is the direction of water flow reversed?

 

So the cool side of manifold is still the same and vice versa? Otherwise won't the actuator sense the temperature differential back to front so to speak and then just open the actuator fully in the hunt to achieve the 4degrees but never get it and in effect just be wide open

 

 

The flow remains the flow, but is cool, rather than warm, so in cooling mode, instead of the return being 4 deg C cooler than the flow, it's 4 deg warmer.  I was surprised to find that these actuators worked the same in cooling mode, but I guess it's just a function of them not caring which way around the sensors are clipped on.

[Dan F]

7 minutes ago, Jeremy Harris said:

The flow remains the flow, but is cool, rather than warm, so in cooling mode, instead of the return being 4 deg C cooler than the flow, it's 4 deg warmer.  I was surprised to find that these actuators worked the same in cooling mode, but I guess it's just a function of them not caring which way around the sensors are clipped on.

 

That's pretty neat. Are you monitoring temps yourself somehow, or do these tell you temps? Not questioning your conclusion, just wondering how you know..

[Jeremy Harris]

14 minutes ago, Dan Feist said:

 

That's pretty neat. Are you monitoring temps yourself somehow, or do these tell you temps? Not questioning your conclusion, just wondering how you know..

 

 

I log the temperatures on the house data logging system, but also have a couple of digital displays on the UFH wiring centre, so can use these to do a quick check:

 

[Jeremy Harris]

Just taken a photo with the floor cooling running, which shows the flow temperature cooler than the return: