Sizing Power Supply for Caleffi Manifold Actuators

SENWiEco

Good day gurus!

I have spent the evening researching on this site, and others, what I need in terms of a power supply for my manifold actuators and my head now hurts and is spinning.

Here is what I have installed (and before I am told to change it, drywall is already in place and house is finished), I now realize it may have not been best way to do this and would have been better to have broken up power supplies and/or used a controller.

Anyway, I have 5 manifolds over three levels of the house. There is a total of 34 loops connected to these manifolds spanning 17 zones. I am using 34ea Caleffi 656404 actuators (no end switches) that consume 250mA in rush, 125mA holding current and consume 3W running power consumption.

The power supply circuit for these manifolds is a single daisy chained 18/2 cable starting in mechanical room and routing past each manifold.

The actuator controls have been wired up to allow for individual T-Stats in each zone (for a conventional approach), but while I am in dwelling, they will be controlled by 5ea iStat6 devices, with each connected with up to 4 remote temp sensors located in the rooms controlled by that iStat6 (all 4 remote zones controlled by the one iStat6 + it will also control the room zone the iStat6 lives in). The main living zones, on the main two floors will all have same room setpoints.

Due to the high performance of this home (total 11,400 BTUH for 2850 ft2 of living space), it is highly unlikely that even 1/2 the zones would call for heat or cooling at same time. I could see all the southern zones calling for cooling at the same time on a very hot summer day, which would be 5 zones and 12 actuators. The heating side of things would be a lot more spread out as many rooms have enough internal gains to prevent heat ever being needed in them, when they are in use. My office for instance, is currently 24ºC (75ºF) and it is 4ºC outside, and I have yet to put any heat in this room since I moved in on Sept 13 (there is no central heat in house yet, we are heating house with one 1500W heater on each floor turned to med - 1000w).

I have seen comments like, just calculate for operating current, as transformers can take 200% of rated load for small periods, so don't worry about in-rush current. But don't know if this is good advise.

Can someone weigh in on the 24V DC (or should I do 24VAC) transformer sizing I would need to feed all 34 actuators, or point me to online literature I can review?

I would very much appreciate it and am thankful for all the assistance I have received on my project!

In case it matters, here is a small table identifying number of actuators(loops) in each zone.

Z101 = 2
Z102 = 1
Z103 = 4
Z104 = 1
Z105 = 2
Z201 = 4
Z202 = 2
Z203 = 2
Z204 = 1
Z205 = 2
Z301 = 3
Z302 = 3
Z303 = 2
Z304 = 1
Z305 = 2
Z306 = 1
Z307 = 1

Jamie Hall

First place, most heating circuits are 24 VAC. 24 volts rectified to DC is vanishingly rare.

I presume the 18 gauge wire is already in place? That's a shame. You should have looked it up first. The maximum current capacity of 18 gauge wiring for continuous power supply is 2.3 amps, and on occasions -- which have to be considered -- your system will draw 4.25 amps. If you used a quality wire, with high temperature insulation... it might fly.

In terms of what to power it with, to avoid frying the transformer, you will need at least a 120 VA transformer, and a 200 VA transformer would be better -- they will handle a 200% overload, briefly, but they aren't happy with it.

Zman

Is there a 120-volt circuit near some of these manifolds where you could set a remote transformer?
I agree that they won't normally all call at the same time, after a power outage they sure will.
24 VAC is what you want to run.

EBEBRATT-Ed

Yeah, should have been a seperate cable to each manifold. This frequently happens with low voltage wiring people think "it's just 24 volts" but the same rule of voltage drop and amp draw apply.

Hook it up as is (with the correct size fuse installed) and hope the diversity of only a few zones calling at once keeps the fuse from blowing. (I doubt this will work)

SENWiEco

Thanks guys - yes I screwed up! I did pass design by someone in field at the pre-drywall stage, but guess they missed the significance on the number of actuators I had. I should have know better as I did a detailed load analysis for the main electrical system (which included 24VDC circuits for LED lighting). Yes, I just was thinking "it's just 24 volts" and that the loads (in mA) were so small, they would not add up to much. Stupid mistake. I will be sure to put some of this info on my site so other home owners can learn.

Good news is I DO have a source of AC beside 4 of the 5 manifolds (thanks @Zman) , so I will be able to run independent transformers beside most of them.

So what should I be using for the vA requirements of each actuator?

Many Thanks

Zman

For us mortal electrical folks VA and watts are the same thing. If you multiply your amps x volts, you will have your answer. I like to oversize transformers by ~30% because they last longer and you will have the extra capacity for smart t-stats and all. Having a circuit breaker on the transformer is also a nice feature, especially for DIY folks.
https://www.supplyhouse.com/Functional-Devices-TR75VA001-Transformer-w-Circuit-Breaker-Foot-Single-Threaded-Hub-Mount-75VA-120-to-24-Vac

hot_rod

It's rare that anyone sizes the transformer for all actuators calling at the same time. Although after an extended power outage it is possible they could all hit inrush current draw at the exact same time. If you use quality transformers they can take an occasional over-load.

If you use the formula high draw ZV like the gold tops would need a 40Va transformer for each valve! 1Ax24V, but you commonly see 3 on a 40 Va transformer without an issue.

Caleffi suggests 9 of the low current draw on a 40 Va. Use Caleffi zone control and you have 80Va across all the connections. Some relay boxes split the 2 transformers, half the connections on on, 1/2 on the other.

When you are loaded up on thermal actuators, nice to have a lot of Va available.

Also be aware of the power requirement of some t-stats, if the same transformer powers them. Some stats can draw down a 40 Va when they go into battery recharge mode.

Zman

Hot rod makes some good points. One of the reasons I like to oversize has to do with the lack of air density at high altitudes (electrical components don't cool very well). That issue does not apply to most folks...

SENWiEco

Thanks Bob, @hot_rod so based on 40VA divided by 9, you are allowing 4.44VA load per actuator. I will add up the loads per manifold and install a suitably sized power supply at each (total plus ~30%). Many thanks all for everyone's help!

SENWiEco

@Jamie Hall you mentioned "The maximum current capacity of 18 gauge wiring for continuous power supply is 2.3 amps" Can you provide a definitive source I can use as a reference for this. Max Amp for a 18/2 based on 24VAC and a distance chart? I see it can handle up to 16A if very short (under a foot), but have been unable to find a source that prorates the load based on cable length

offdutytech

If you need ample 24vac power with the ability to have multiple circuits that are fused Functional Devices has several models. When I did DDC controls we used these for vav box power trunks and control valves for central plants. We always tried to load each circuit at no more than 85% capacity to allow for safety factor.

https://www.functionaldevices.com/products/building-automation/details/PSH200A/

EBEBRATT-Ed

@SENWiEco , here is a voltage drop calculator

http://wiresizecalculator.net/calculators/voltagedrop.htm

From the power supply to the end the maximum voltage drop allowed is 5% at full load

5% of 24=1,2 volts

SENWiEco

@offdutytech - thanks for the link, yes this would have been great IF I had properly planned the system before drywalling. Unfortunately I only have the single 18/2 cables daisy-chained from manifold to manifold. I now have to abandon this cable and am looking at zone control at each manifold.

@EBEBRATT-Ed - thanks for the link!

offdutytech

You can always use wire duct and surface mount it for a clean look. This is used in control cabinets 

https://www.panduit.com/en/products/wire-routing-management-protection/wiring-duct-accessories/wiring-duct-duct-covers/f2x3lg6.html

SENWiEco

thanks @offdutytech - Yes I am using some of this for my control cabinet. But the 5 manifolds are spread out over three stories, so not an option for those. But thanks for the thought.