Zone control help

pch

I need to control both a high temp, and a low temp zone, each with its own pump. I don't want the high temp zone to be the priority zone, because eventually I will need to replace my MZ boiler and the replacement may not directly support priority DHW.

I have an old Tekmar (337) Dual Zone Manager (no longer manufactured). The Tekmar supports two groups of 3 zones; each group has its own pump. However, I cannot see how to make it work in my system since I need 4 LT & 1 HT, not 3 & 3 zones. Also, since it has been discontinued, I don't want repair/upgrade issues.

From their descriptions, it looks like I might be able to use a Taco or Caleffi zone controller, but I don't see how to control the two different pumps, one for the high temp fan coil, the other for the in-floor radiant, while retaining support for future changes: when the MZ is replaced, the new boiler may not have a built-in circulator, so I need to plan for control of that as well.

My system...

Current system configuration (in use):
- Condensing, non-modulating boiler (Monitor MZ25), 95K BTU. Boiler has built-in pump. Pump comes on and boiler fires when t-stat calls for heat, or there is a (priority) DHW call.
- Priority DHW: HW tank calls for heat, switching boiler to priority mode; boiler sends signal to A/B valve, redirecting flow to HW storage tank.
- High temp zone, fan coil: 5 ton SpacePak air handler ducted to every room. T-stat signal is sent to the SpacePak which relays it to a single zone pump controler. The zone controller forwards the signal to fire the boiler, and starts the zone circulator. The fan coil supply line has an aquastat attached just before the SpacePak; when the water temp is high enough the aquastat turns on the fan.

Expanded system (parts in progress):
√ Near boiler piping reconfigured to provide primary/secondary loops.
√ 30 gal. Boiler Buddy: Installed in the system as the primary loop, low loss header, and buffer. The boiler supply temp is set high enough that it satisfies the (high temp) SpacePak.
- Low temp, in-floor radiant zone: About 2000 feet of 3/8" Onix tubing split into four zones, each controlled by a zone valve and t-stat. A Grundfos pump circulates water to all zones. Radiant floor water temp is managed by a Caleffi thermostatic mixing valve. Mixed water flows through a Watts four port manifold with Tekmar zone valves.

hot_rod

A 3 pipe buffer is my suggestion. MZ is controlled by a setpoint controller to maintain tank at whatever temperature you need. It could also be on ODR with a new boiler that has that option, someday. The MZ pump is controlled by the relay in the MZ.

You need a zone valve control relay box to run the actuators on the Watts manifold. A zone switching relay to run the high temperature circ for the SpacePak. Caleffi relays communicate via a 3 wire thermostat wire between them.

If you add an indirect it is on zone one or either relay, for priority. Parallel pipe it before the buffer. Or leave two connections for future indirect..

Either the pump relay box or the zone control box turns on the appropriate circ.

I would still add a good air sep of the MZ between it and the tank.

A 3 pipe buffer is the best mix of a 2 pipe and 4 pipe.

Direct to load supply, buffer is only involved when loads are smaller than MZ output. Buffer gets charged when all loads stop.
Next call for heat comes from buffer until it drops in temperature.


Return temperature to boiler is always as low as possible, straight across bottom of the BB, no tank blending.
The tank is still involved as a buffer for the MZ as return crosses the tank, but stratification is not effected as it is in a 2 or 4 pipe.

pch

I just watched a Siegenthaler video about 3-pipe buffers: I had not heard of them. Currently my BB has four pipe connections. I can repipe to 3, but probably not until warm weather - can't go without heat now.

Buffer questions:
1. BB has 1-1/2" ports which have bushings/fittings down to 1" copper. Should the 'header' going into the tank be 1-1/2" over the length where the load take-offs are?
2. How close should SP and radiant take-offs be to each other and to BB?
3. Should I put a check valve between the boiler and BB on supply side?

You need a zone valve control relay box to run the actuators on the Watts manifold. A zone switching relay to run the high temperature circ for the SpacePak. Caleffi relays communicate via a 3 wire thermostat wire between them.

I haven't quite grasped this yet...
So, do I simply need to connect the zone valve controller and zone pump controller via the communication wire? Is it that simple?

hot_rod

So the BB is already piped into the MZ? Four pipe tanks will work and give you the buffer and hydraulic separation. The 3 pipe will allow direct to load, and lower return to the boiler, so a few additional benefits. It may not be worth a repipe?

Direct to load, basically if the MZ if flowing 10 gpm to the BB and both distribution pumps are running and moving a total of 10 gpm, no flow goes into the top of the tank, supply from MZ all goes directly to the system. The return just crosses the bottom of the BB, this is how you get the lowest return temperature to the boiler

When the distribution is not needing 10 gpm, call it 6, then 4 gpm goes into the top of the tank and starts heating it up. It heats until it reaches the desired temperature.

Whatever the hi temp SpacePak requires is what you will maintain the tank temperature. A sensor in the top of the tank from a setpoint control is now running the MZ. It doesn’t need to communicate with the heating thermostats. Its only job now is to keep the BB hot. And DHW via the combi function.

If you go with a 3 pipe the upper supply pipe from the buffer needs to be 1-1/4, same for the lower return connection. Upper right BB connection gets capped off.

Yes the connections should be close to the tank and close to one another. 18- 24” is plenty of pipe off the BB to make all the connections.

The large pipe at the tank connections allows the various pumps to get adequate flow and not interfere with one another. One of the reasons it has large connections.

So the single pump controller just needs to turn on the high temperature pump. BB is hot, ready to go.
An additional zone valve controller will power your manifold actuators and power the low temperature pump. They would not need to communicate, as long as there is no priority for an indirect

If someday you switch to a non combi and add an indirect, you need a 3 rd pump and for the two heating
pumps to communicate. I’m not sure what your plans are when the MZ gives up? Or how much piping you want to add for a future indirect?

pch

Potential configuration change to 3-pipe buffer tank:

The 3 pipe will allow direct to load, and lower return to the boiler, so a few additional benefits. It may not be worth a repipe?

Yes, the MZ handles priority DHW; I do have an indirect HW tank. Biggest concern is the boiler cycling. Even with the BB installed, the boiler cycle is about 60-90 secs; this was right after getting things going (again) and not at all what I expected to see. I have since set the MZ circulator at its lowest speed to reduce flow rate into the tank and hopefully get better stratification. Next week I will put thermostats on the boiler supply and return to see what the delta-T is. Any other suggestions?

Considering future DHW (without the MZ), and limiting boiler cycling, the 3-pipe buffer configuration may still have a good work/benefit ratio.

Boiler control:
A more immediate question is something I probably should know, but...
The SpacePak zone is currently managed by a single zone pump control which turns the pump on and fires the boiler. I will add a 4 port zone valve control for the in-floor radiant, which will turn on its pump and fire the boiler. So, both a zone valve control & a zone pump control might want to signal the boiler at the same time. It's not clear to me how to manage (wire for) that. Can the boiler TT/RW contact be connected to both controls at the same time, or do I need some relays?

hot_rod

The Boiler Buddy should be the only thing that turns the MZ boiler and its pump on, via a control like this Ranco. Think of the BB as just an extension of the boiler.

The sensor from the Ranco goes into or against the bare metal near the top of the BB. Or maybe the BB has a sensor well?
The contact NO & COM terminals in this Ranco connect to the TT connections in the MZ, with low voltage thermostat wire..

The boiler only fires when the tank temperature drops to your low temperature setting.

The Ranco allows you to set a differential. So the MZ runs until the BB gets to say 160 or whatever the highest temperature you need for the SpacePak. If you set a 15° differential the MZ fires back on when the tank drops to 145.

When any thermostat calls it either turns on a pump, or opens radiant actuators and starts that pump, via a zone controller. The thermostats do not need to connect to the MZ anymore. The Ranco operates the MZ now.

Flow will come from the hot tank until it drops to the low setting, 145 in this example. When the boiler fires, flow may go directly to the load, or some to the tank, some to the load. That depends on the GPM requirement at any time.

If you widen the Ranco controller to a 20° delta 160- 140, then you get more drawdown before the boiler fires again. And the boiler runs longer to recover the tank, because you ran it down to a lower temperature.

I'm confused is the MZ a combi, supplying both heat and DHW or do you have an indirect for the DHW? Or both? Combis will short cycle on low DHW loads, no way around that, since the MZ doesn't modulate.

The zone controller that controls the SpacePak pump on and off needs to disconnect from the MZ. It still turns on the pump, but only the Ranco turns on the MZ

A sketch of how the indirect is piped into the system. Also is there a specific DHW connection in the MZ? Or what tells the MZ to fire when the indirect needs heat?

Typically an indirect does not need to connect to the BB buffer. Pipe it as a parallel circuit so the MZ can feed it directly.

I don't remember which MZ you have? If it is a 140 I would pipe the indirect with at least 1" and pump 10- 12 gpm, from the MX to the indirect let the indirect take all the MZ can give to the tank.

pch

The Boiler Buddy should be the only thing that turns the MZ boiler and its pump on, via a control like this Ranco. Think of the BB as just an extension of the boiler.

Mind blown 🤯 Now I understand.
The Boiler Buddy does have a dry well, mid tank. However, it is 1/2” diameter and the ETC control’s sensor is 1/4”. Now, I need to find a dry well (bulb) adapter. Is there such at thing? I chatted with folks at SupplyHouse and looked online, but came up empty.

Boiler is the MZ 25C. It supports a priority DHW mode. An indirect tank is parallel piped and flow is diverted from the buffer tank via an A/B valve controlled by the boiler. Sensor in the tank signals boiler to heat the tank.

HomerJSmith

Just put a lot of heat conducting paste around the sensor and put it in the well as far as it will go.
Silver heat conducting paste is best. It is used on computer heat sinks.

pch

👍. Thanks for your help!

hot_rod

Or take a short piece, 4" of 1/2" copper tube. Split it lengthwise with a hack saw. a bit of taper in the split. Slide it in ith the sensor, it acts as a wedge to keep the small sensor in contact,

Some Honeywell cap. tube controls come with a thin brass wedge like that to keep the sensor tight against the well. It has a bent end so you don't push it in too far and lose it

Actually the sensors work just a well in contact with the outside of the tank. Slide it in between the foam insulation and the steel tank.