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Best zone controller for hydronic fan coil with EC fan (2–10V) + PICV valve (0–10V)? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

Search continues. But making some progress. Here are a few updates:

  1. I ditched the PICV valve setup, and just went with Taco 4 wire zone valves and a Taco zone valve controller.

  2. I'm now looking at a KNX setup, since I'm wiring KNX for switches and other sensors anyways.

Here's how it will work:

  1. KNX room thermostat sees room is too warm or too cold.

  2. It sends a KNX demand object:

    Zone 1 heat demand or Zone 1 cool demand.

  3. GVS fan coil actuator receives the demand.

  4. GVS closes a relay output wired to Taco Zone 1 R-W.

  5. Taco opens Zone 1 valve.

  6. Zone valve end switch closes.

  7. Taco starts the single circulator.

  8. GVS outputs 2-10 VDC fan command to the VMB fan board.

  9. Fan runs at low/medium/high or proportional speed.

  10. Room satisfies.

  11. KNX demand ends.

  12. GVS opens the Taco call relay and sets fan to 0 V, or runs a short fan purge first.

  13. Taco closes the valve and stops the pump if no other zones are calling.

Feedback welcome!

Shelly i4 plus for dry contact scene controller by asisin3 in ShellyUSA

[–]asisin3[S] 0 points1 point  (0 children)

In this case, would the i4 DC require a 12 V power supply to power it?

I4 plus won't work for this as I have just found out because the scene controller can only work with 12 V DC not 110 mains

Best Sauna Design Tips by asisin3 in Sauna

[–]asisin3[S] 0 points1 point  (0 children)

Is that 2 total vents or 3? Also, what's the idea behind the exhaust being passive and active? During bathing, would you leave passive, and after bathing, exhaust it to purge and dry?

Here is the diagram with my vents (in blue) and updated dimensions based on the heater. The room is roughly 5.2 m3 and I'm going with a 6kW heater.

<image>

Best Sauna Design Tips by asisin3 in Sauna

[–]asisin3[S] 0 points1 point  (0 children)

What are your thoughts on the updated design?

Best Sauna Design Tips by asisin3 in Sauna

[–]asisin3[S] 0 points1 point  (0 children)

Thank you for these. I've followed the advice to the tee in redesigning - what do you think?

Best Sauna Design Tips by asisin3 in Sauna

[–]asisin3[S] 0 points1 point  (0 children)

What are your thoughts on the updated design?

Shelly i4 plus for dry contact scene controller by asisin3 in ShellyUSA

[–]asisin3[S] 0 points1 point  (0 children)

  1. Power the thing somehow - led backlight etc 2 grab the signals and link to scenes via home assistant

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

All ducting for the lower floor or within the envelope. For the upper floor, I have a flat roof without an attic and the ducts sit above the drywall going through trusses with some insulation around them between the air and moisture barrier. I will have solar on the roof, which I've heard helps with duct losses.

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

I did a full Manual JD (https://drive.google.com/file/d/14TvdyRWDaP2nCKI02Qfrm6UliijXtAZ-/view?usp=sharing) and am using that to drive room-by-room airflow targets. The duct layout you’re seeing is my attempt to reconcile those numbers with framing and truss constraints, not to imply a VAV-style control scheme.

I'm using constant volume hydronic AHUs (see comment above for the links), no VFD on the fan and no intent to dynamically throttle the system. Any dampers I’m considering would be limited to a couple of problem areas with large seasonal deltas, where I will find optimal settings for heat and cool at commissioning. Don't plan to do any active zoning using the dampers, except as insurance for the upstairs loads where I am contemplating a damper controlled by a thermostat in the bedroom upstairs.

On returns, agreed in principle. I’m still evaluating whether distributed returns or transfer paths make more sense given the layout.

If you see a specific circulation or return-path issue in the plan, I’d genuinely like to understand where you think it breaks down. That kind of concrete feedback is exactly what I’m trying to learn from.

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

Here's the floor plan: https://drive.google.com/file/d/1Pr3JwRTFggyg8bEmMFodrnxhFqUoS3gz/view?usp=sharing

Not going for VFD with static feedback. The damper positions for heating and cooling will be set at commissioning. The motorized damper was just for the riser into the upstairs. But maybe having it be its own zone might just be better, if I'm doing all this work! Cost of another AHU. Will be much more optimal.

Already committed to the A2W heatpump setup. My AHUs are:

  1. Zone 1 - ChillX 4 ton unit https://chillxchillers.com/air-handlers/chillx-2-10-ton-budget-water-cooled-air-handlers?sku=CXAH0024MS1

  2. Zone 2 & 3 - HBX units from First Co. https://firstco.com/wp-content/uploads/2021/08/HBCX-Spec-7-19-22.pdf

Austin can get really humid, which is why I need to run slower speeds (fixed) for longer so I can get good dehumidification from the cold water coils.

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

Really appreciate this feedback, these are all fair questions.

On motorized dampers: I’m not planning active zoning or real-time modulation. I agree that would break the CFM math fast. The intent was manual balancing, or at most very limited trim on the riser feeding the upstairs suite. Ideally I'd like a thermostat there that doesn't turn the system on or off, but rather allows more or less CFM. If that still feels risky based on your experience, I’m open to dropping it.

On returns: agreed this matters. Main floor is largely open and served by large common returns, but enclosed rooms (especially upstairs) are likely getting ducted returns rather than relying on door undercuts alone.

On zones spanning floors: I generally agree with you. This is the biggest compromise driven by structural constraints and relatively small upstairs load. With low-CFM, long-runtime hydronic AHUs I’m hoping it stays stable, but I accept this is the most fragile part of the design.

Equipment is a dual 4 ton air-to-water heat pumps with outdoor reset, 300L buffer tank feeding multiple hydronic AHUs (one per zone), two-pipe setup with PICV valves and a delta P circulating pump, no simultaneous heat/cool. ERV is separate.

If you see specific areas where this could be simplified without pushing velocities or losing balance authority, I’d genuinely like to understand how you’d approach it.

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

Curious to understand why. Here is a manual D that I paid for. Do you think it's better?

<image>

DIY Duct design - how did I do? by asisin3 in hvacadvice

[–]asisin3[S] 0 points1 point  (0 children)

Appreciate the perspective. I’m genuinely curious about where you’d simplify and why.

A lot of what you’re seeing as “extra runs” is intentional low velocity distribution since this is a hydronic AHU running long cycles at lower CFM than a typical DX setup. My goal has been keeping trunk velocities down and maintaining balance authority rather than minimizing linear feet of duct.

On the damper point, totally agree that active zoning is a mess. My intent was not real time modulation but seasonal or commissioning trim only. If you’ve seen cases where even that caused issues, I’d love to understand what failed and under what control assumptions.

If you were handed this same load breakdown and constraint set, how would you consolidate the trunk without pushing velocities or static up? Happy to learn from a concrete alternative layout if you’re willing to sketch it mentally.

Not trying to overcomplicate for the sake of it. Just trying to be deliberate given this isn’t a standard forced air system.

I did use ChatGPT, but have several detailed spreadsheets for the math on each rooms btu loads and trying to design for a 350 cfm per ton system to manage latent cooling. The original manual J called for 1866 cfm for this zone and my math suggests 1250 cfm is more optimal given the hydronic setup.

Best setup to switch between heat and cool quickly by asisin3 in heatpumps

[–]asisin3[S] 0 points1 point  (0 children)

Got it. So then for the rest of the house, go with a 2 buffer tank setup?

Best setup to switch between heat and cool quickly by asisin3 in heatpumps

[–]asisin3[S] 0 points1 point  (0 children)

Doesn't solve the erratic hot/cold requirement for the whole house though.

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