My central hydronic floor heating system uses electricity as power source.
It only has the heater temperature setting automated,
everything else is set manually now - the water pump for
a floor is manually turned on and manifold valves for each zone
in a room are opened manually.
For a start I would like to automate the sensing of temperature in a
room (wifi thermostats) and switching of manifold valves
as needed for heating and because the heater does not
have the capacity to heat all zones at once.
I will start by digging around the web to see what others have done,
but before that I have two questions:
(a)Is it better to buy the manifold valve actuator in 24V or 230V versions
i.e. which is better/easier to interface ?
(b)I'm not sure how often zone switching needs to be done per hour
but I'm concerned about the lifetime of mechanical relays for this
application. One relay board I checked on ebay showed 100K switches
as life of relay. Not sure what sort of switching figures
SSR's have. Secondly, frequent switching will cost in power usage -
are there any good ideas about using latching relays - any pointers
on relay boards to use (I have the manifolds with 9, 8, 5 and 4 actuators on the
floors)?
(a). No Arduino can handle either voltage directly, so you'll need external hardware to switch it. From that point of view either will do. However, mains voltage is potentially lethal unless you know what you're doing. Since you're asking the question therefore, go with 24V
(b). SSRs can expect a much longer lifetime than anything mechanical. Make sure you heatsink or otherwise keep them cool per the data sheet.
I'd expect the manifold settings to be the same for tens of minutes. How frequently do you change them manually?
vjekob, where are you located? There are readily available valves for hydronic heating systems in the US. They use 24VAC supplied from a 120VAC to 24VAC transformer available in the same department in the hardware store.
I'd also go for 24V manifold valve actuators, as the lower voltage is so much easier to handle (and safer, of course). You an use electronic switches such as MOSFETs (if DC; SSRs for AC) to control them. Depending on the current fair chance no heat sinks necessary. Both MOSFETs and SSRs have no moving parts, so as long as they're used within specifications they'll last very long.
Indeed switching would probably be in the tune of every half hour or so. There's likely a long delay between switching a manifold and the heat coming out in the room.
WiFi thermostats - why WiFi? It may be more convenient to use 433 MHz or 2.4 GHz direct links. If you want to go the WiFi route, do check out the ESP8266 based systems - the NodeMCU and WeMOS mini development boards have them.
Thanks for all the input - I'll take it step by step:
For the manifold valve actuators - I need 26 pieces as follows
on different floors (8 - Floor 3, 9 - floor 2, 5 - floor 1, 4 - floor 0).
The spec of the Rehau actuators is as follows:
230V model : 230 V, AC +10 %... -10 %, 50/60 Hz,
Turn on current 300 mA for max. 200 ms
Power 1.8W, Without power, normally closed contact
Time to open/close 3min.
24V model : 24 V, AC, +20 % … - 10 %, 0 - 60 Hz
Turn on current 250 mA for maks. 2 min
Power 1.8W, Without power, normally closed contact
Time to open/close 3min.
I suspect Danfoss or other would be similar, just need to find out which is cheaper
(maybe someone has gone through this check recently and knows a good
quality/reasonably priced model ?)
Correct me if I'm wrong but if I use the 230V model, then I will be connecting
230V directly to each input of the the relay circuit board. If using 24V model,
will I need one 230V -> 24V transformer (which is an additional
cost ) ? Is there any benefit of the 24V model if each relay has opto coupling ?
If in the US, the wiring and insulating requirements for 24VAC is much less than for 230VAC. That includes both for the building, the project, and the parts in the project. The 230VAC-24VAC transformer is not all that expensive (~20USD)
Can you post a link to these devices, actuators sound like you need an OPEN and CLOSE signal.
The spec of the Rehau actuators is as follows:
230V model : 230 V, AC +10 %... -10 %, 50/60 Hz, Turn on current 300 mA for max. 200 ms
Power 1.8W, Without power, normally closed contact Time to open/close 3min.
24V model : 24 V, AC, +20 % … - 10 %, 0 - 60 Hz Turn on current 250 mA for maks. 2 min
Power 1.8W, Without power, normally closed contact Time to open/close 3min.
vjekob:
Is there any benefit of the 24V model if each relay has opto coupling ?
Yes: safety.
230VAC can kill you easily. 24VAC not so much.
Reason to use higher voltage: lower current so thinner cables/less cable losses. Doesn't seem to be an issue for your low-power devices and short transmission distances.
so it only requires one signal/power to close the valve.
OK, so I'll go for the 24V model for safety using a Rehau alternative
(Rehau is expensive and have found forum info on failure, so no point in
paying so much - even looks same as some others, so probably
produced by someone else) with M30 x 1,5 thread.
Here's one: https://itsolution.lindab.com/lindabwebproductsdoc/pdf/documentation/comfort/lindab/technical/actuators.pdf
From the above doc, the 24V transformer is specified via formula n * 6W (n = number of actuators)
For my application :
Floor 3 - 8 actuators / 48W transformer
floor 2 - 9 actuators / 54W transformer
floor 1 - 5 actuators / 30W transformer
floor 0 - 4 actuators / 24W transformer
OK, now I need the relay board and then try something out. On ebay
I found these SSR boards with 6 relays (and other with 4 relays), so I'll need 2 pieces for
9 actuators and see if there's anything special in using the two together.
So go for a set 2x 50-60W and 2x 80-100W transformers, especially if you need to run all valves at the same time for longer periods of time. That keeps the heat down. Higher power rated ones shouldn't cost that much more.
