Current draw of a wax solenoid?

[MJNewton]

No, it's not as off-topic for this sub-forum as it sounds!

 

I've been playing around with measuring and graphing various operational aspects of my MVHR installation - temperatures, humidity etc.  I am also measuring power consumption and whilst the system is up and running it's not fully set up yet so don't read too much into the absolute power figures. I'm measuring ~7W at 'idle' and ~40W during 'boost' but have noticed on a couple of occasions a ~12W idle figure and thought there might have been a controller problem (ie fan speed not returning to low enough).

 

Then it dawned on me; when looking at the associated temperatures during these periods it could well be that the 'summer bypass' feature is  kicking in and the extra ~6W is down to that. I know that the summer bypass on my unit (Titon 1.25 Q Plus HMB Eco) consists of what appears to be an electrically operated (heated) wax solenoid that closes (or is it opens?) a grate to bypass the exhaust air around the heat exchanger but I didn't expect it to take 6W to operate such a thing? I *think* it runs off 12v DC.

 

I suppose it doesn't really matter, but given it doubles the base load it did get me thinking. That said, when fully installed and configured my base load may well be much higher and so the increase - relatively speaking - will be less.

Edited April 8, 2020 by MJNewton

[Jeremy Harris]

6 W sounds reasonable for a fairly powerful/wide movement range wax stat.  UFH actuators are probably a fair bit less power (tiny range of movement and modest force) and they tend to be around 2 W to 4 W.

[MJNewton]

Ah okay. I think I was assuming that one of the reasons they are used is that they are really low power so it just struck me as being rather higher than I expected. Having just done some cursory searching on the subject though I didn't find a single mention of their power consumption but rather just how strong and reliable they tend to be, hence presumably why they are well suited to this application. 

Edited April 8, 2020 by MJNewton

[Jeremy Harris]

7 minutes ago, MJNewton said:

Ah okay. I think I was assuming that one of the reasons they are used is that they are really low power so it just struck me as being rather higher than I expected. Having just done some cursory searching on the subject though I didn't find a single mention of their power consumption but rather just how strong and reliable they tend to be, hence presumably why they are well suited to this application. 

 

 

Just looked at an old UFH actuator and the label gives the power consumption as being 3.5 W  It seems to move by about 4 or 5mm at a guess, so not much.

[MJNewton]

This bypass is a nearly-A4 sized 'hit and miss' metal vent and it I think it needs to move around 10mm and so, as you said, 5-6W sounds about right (perhaps even on the low side!) when compared to the UFH actuator.

 

 

Edited April 8, 2020 by MJNewton

[SteamyTea]

Does it stay permanently on when in summer bypass?

 

I have not heard of these.  Are they like a traditional waxstat but with a heating element in them?

[MJNewton]

11 minutes ago, SteamyTea said:

Does it stay permanently on when in summer bypass?

 

I have not heard of these.  Are they like a traditional waxstat but with a heating element in them?

 

Yes, when heated by the element the wax expands resulting in linear motion. With power removed it cools and a spring pushes the whole thing back (I guess the contraction is insufficient to pull things back by itself). 

 

Also often used in washing machine door interlocks I believe as even if the power is removed it still takes a few seconds to retract and open thus allowing the spinning drum to come to a stop. 

[SteamyTea]

5 minutes ago, MJNewton said:

Yes, when heated by the element the wax expands resulting in linear motion

I guess they are reliable, not a very good solution, really needs a stepper or servo motor I would have thought.

 

1 W has the ability to move 1 kilo, 1 meter every second.  How heavy is the baffle.

[Jeremy Harris]

Here's a couple of photos of a typical UFH wax operated actuator.  This one has a 3.5 W heating element that takes around 5 minutes to fully open the valve:

 

 

 

[SteamyTea]

9 minutes ago, Jeremy Harris said:

Here's a couple of photos of a typical UFH wax operated actuator.  This one has a 3.5 W heating element that takes around 5 minutes to fully open the valve:

 

So 3.5 [W] x (5 [min] x 60 ) = 1050 Ws = 0.00029166666666667 kWh

Don't seem to so bad when preceded with lots of zeros.

Edited April 9, 2020 by SteamyTea

[dpmiller]

but it's energised the whole time it's actuated...

in saying that, there could be a bit of PTC involved