Question!

adambuild

Simply curious: Why are zone valves not full port, but instead they have various CV restrictions? What is the reason / logic? Thanks in advance

EdTheHeaterMan

Answer!

Because that is how we always made them . And the slight restriction from a small diameter opening that is all of about a millimeter is length hardly matters in the entire 50+ foot long loop of 3/4" copper.

EBEBRATT-Ed

The bigger the opening in the valve the larger the actuator you would need. Zone valve are made with a significant Cv which can offer a lot of restriction.

I had a job that was a typical 5 room ranch with an 1 1/4" Monoflo loop. No zone valves. When the boiler was replaced an indirect was installed. The heat loss of the house was only 50,000 btu so 5 gpm was all that was needed. Two 1" zone valves were installed one for the indirect and one for the heating loop. 1" valve were used as there was no reason for the expense of 1 1/4 valves as the indirect called for 1" pipe and the heating loop only needed 5 gpm. 1" is good for 8 gpm.

We installed Honeywell zone valves and as I recall the cv was like 4.5-5. The heating loop was very sluggish to heat. The indirect with shorter piping was fine. We took the Honeywell valves out and installed Taco with a cv of 8 and everything was fine.

GGross

CV is a rating specific to control valves, even if the valve were "full port" it would still have a CV rating. That being said if you would like a less restrictive valve most brands offer them as a higher CV option, standard honeywell zone valves are something like 3.5 CV for, they offer the "full port" version that is 8CV

Sylvain

Any conduit, even a 1 foot straight pipe will have a pressure difference between its entrance and its exit wich will depend of various factors.

Valve Flow Coefficient (Cv) is a valve’s capacity for a liquid or gas to flow through it.
It is technically defined as “the volume of water at 60°F (in US gallons) that will flow through a valve per minute with a pressure drop of 1 psi across the valve.”

Have a look here for example:
https://kimray.com/training/what-valve-flow-coefficient-cv

Dave H_2

And here is the quick and dirty answer.....because it doesn't need to be full port!

Now the real answer behind the above, it also costs alot more to manufacturer to make the ball and valve housing the same size as the inside diameter of the pipe. The Cv is a way to describe what the pressure drop is across the valve. The high the number, the less of a pressure drop.

Here is an example, the 3/4" Zone Sentry has a Cv of 10.2. It means if you were to pump 10.2 gallons per minute thru it, the valve would generate 1 psi of pressure drop or an equivalent of 2.31 foot of additional head loss to the system.

This Cv is very high since the max, safe, trouble-free flowrate in a closed loop hydronic system thru 3/4" copper is 4 gpm. This pressure drop would be very low.

We did a Taco Tuesday webinar on this and you can watch it here

hot_rod

I also has to do with the shut off pressure when talking about spring return type zone valves.
Here are the different bodies that Caleffi offers. Cv from 1- 7.5
Notice the lower the Cv the higher the shutoff pressure. This is because the opening, the orifice is smaller, so it is easier to shut off flow.

Typically low Cv valves are shipped with air coils or packaged units as the manufacturers do not often know what pumps will be flowing the system.

Low Cv valves go to Magic Air, First Co. Whalen, etc, for fan coil kits.
Low Cv would also be used on a DHW system for it's high psi shut off ability.

Modulating zone valves will often have a characterized ball or shutoff cartridge, Belimo, Johnson Controls, etc

Doug_7

The Cv of a zone valve is to help balance the flows in a multi-zone system. Each zone will have a design flow rate, and it is not desirable or necessary to have too high a flow rate, which results in too low a ∆ T.

Imagine a designed system with 8 zone valves. When the first zone valve opens, you would like it to take 1/8 of the available flow, and when the second zone valve opens, you would like it to take 1/8 of the available flow - and so on. The Cv helps regulate the flows through the zones.

If all zone valves were full-port the flow would often be much higher than required or desired.

Imagine a designed system with 0ne pump and 100 zone valves.

Doug

Sylvain

Doug_7 said:

Imagine a designed system with 0ne pump and 100 zone valves.
Doug

Of course this is only a pedagogic example; who would do that?

On the other side, a low Cv means more (pump) energy dissipated in the valve.
There is an optimum to be found. Installation cost/running cost.
How many zone on a single pump? One pump per zone? Which type of pump?

Doug_7

Sylvain said:

Of course this is only a pedagogic example; who would do that?

On the other side, a low Cv means more (pump) energy dissipated in the valve.
There is an optimum to be found. Installation cost/running cost.
How many zone on a single pump? One pump per zone? Which type of pump?

No - this is the actual heating system design in a multi-family building, which is a very good teaching example - because it is the optimum system design.

The in-floor heating system in the multi-family building in which I live has one single pump, to pump the floor-heating water to approximately 170 zone valves - about 8 zone valves per suite in 21 suites.

The single pump is a 3" ECM Smart-Pump that draws about 120 watts while maintaining a ∆P of 5 psig as it delivers warm floor-heating water to the entire building. As the zone-valves open and close, the Smart-Pump simply maintains the 5 pig differential pressure. Do not over-estimate the theoretical energy dissipated by the valve. Do add up the actual total pumping energy.

This single-pump heating system design provides the lowest installed-cost, and the lowest operating cost, compared to any multi-pump system you could envision. Why would you want to install 21 pumps - one per suite - or 170 pumps - one per zone ?

hot_rod

I've never heard of using different Cv zone valves as balancing devices, if that is what you suggest?

With a delta P circ, just use the highest Cv zone valve and the circ has less Dp to contend with. What would a 1 or 2 Cv valve add to that system?

A zone valve with a PIC would be a much better option, for balancing to the exact flow each unit needs. And delta P circs love PICs.

A look at a 1 and 7.5 Cv ZV.

GGross

"Why would you want to install 21 pumps - one per suite - or 170 pumps - one per zone ?"
you wouldn't want 170 pumps by any means, but I can think of at least 2 reasons why you might want to pump each unit individually. First reason, if one pump goes down the whole building doesn't lose heat, just one unit. With a large single pump if it goes down, no heat for anyone. Second reason is that large ECM pumps sometimes have rather long lead times (measured in months recently!), so if that pump goes down it might be down for a while, better install a redundant pump if going with a single. Small ECM pumps equal to a 15-58, are available today at your local supplier allowing for a same day repair. So while you may be able to do it cheaper with a single pump, that does not always mean its the best option

Doug_7

To hot_rod - I did not actually suggest that, but that would be a good design practice.

If for example one zone had a 250 foot loop and another zone had a 50 foot loop, you should consider using different Cv zone valves, to balance the flows to avoid excessive flow-velocities, noise, and low ∆T in the short loop.

All our 170 floor-heating zones are similar in length and use the same Cv zone-valves.

To GGross - Our single 3" ECM Smart-Pump has an on-line spare, so if it goes down the spare starts-up to maintain building heat. Much lower installation cost and much lower operating cost to install a pair of pumps in one location in the Boiler Room, than to install 21 pumps in 21 different locations scattered throughout the building.

In over 25 years of operation this single floor-heating water pump has never failed. The 3" ECM Smart-Pump was installed in 2012 to replace conventional wet-rotor 3-speed pump. So this is a well proven system design for low initial cost, reliability, and low operating cost in a multi-family building.

We keep the heating system water very clean, chemically treated, and filtered to 10 microns. Important to achieving reliable operation and long pump-life.

Adding 21 more heating water pumps would not make our system any more reliable.

mattmia2

I definitely heard of doing rough balancing by selecting appropriate CV zone valves here before, probably from one of the Eds.

hot_rod

To hot_rod - I did not actually suggest that, but that would be a good design practice.

If for example one zone had a 250 foot loop and another zone had a 50 foot loop, you should consider using different Cv zone valves, to balance the flows to avoid excessive flow-velocities, noise, and low ∆T in the short loop.


So in this example what Cv valves would you suggest, assuming .5- .8 gpm?
Seems like a flow setter at the manifold is simpler.

I do agree with the single ECM and zone valves, and some engineers spec N.O. zone valves that open in power outages.

Doug_7

This Topic began with the question: Why are zone valves not full port, but instead they have various CV restrictions? What is the reason / logic?

My answer was to give the reason why you might actually want zone-valves with different Cv's - for example to avoid excessive flow-velocity in a very short loop. So in that case you would be looking for a zone valve with a Cv about half of the Cv of the other normal length loops. That is what the Cv rating is for, but I doubt most heating system designers would bother.

Cv is basically a flow-capacity rating system for control valves, to let the system designer zero in on the best valve selection for the service. Cv is very important when selecting a modulating control valve for a process control system. Much less important for ON-OFF zone-valves in a heating system - but zone-valves still do have a Cv rating.

Agree a flow-setter on the manifold is much simpler and better - if one is available - we don't have them.

As I said: All our 170 floor-heating zones are similar in length and all use zone-valves with the same Cv.

hot_rod

This Topic began with the question: Why are zone valves not full port, but instead they have various CV restrictions? What is the reason / logic?

The answer with any spring return type zone valve is:
The various Cv give you different shut off pressure. A standard zone valve, Honeywell, Erie, Caleffi, WR, etc, is an on off device, not a control valve.

If you have a large base mounted circ in the basement of a multi story, high room type hotel in Vegas, for example, you chose a low Cv valve, high shutoff to assure the 50- 70 psi delta P from the large circ, sized to handle 100's of fan coils, doesn't push past the valve.

If you want to control or adjust flow across a fan coil you would use a coil kit which has a valve that can be modulated, a flow range set, and is also the on/ off control. A standard zone valve would not be the correct choice here.
This 149 coil kit has a PIC function built into the "zone" valve. And you select a flow range when you size it. It can be modulated via an external signal from a BAS for example.

Here is an example why you would not use a low Cv valve on a system that needs flow beyond the Cv. Third top window.

Take a 1 Cv valve and flow 3 gpm across it. Now you have a 9 psi drop to contend with.

RandandReardon

You could just as easily ask why aren’t flow checks typically full port. I would think the simple answer is they don’t need to be. The flow rate in a typical residential ¾” hydronic heating system is 1-4 gallons per minute. The water moves very slow because it needs time in the pipe and radiation to for the heat to chase the cold. Granted the restriction may create a slight increase in velocity across the valve but that would be inconsequential. In a potable water line where the pressure is much higher as are the flow rates the lack of full port will make a tangible difference in flow rate, in a hydronic system it will not.

GGross

RandandReardon said:

The water moves very slow because it needs time in the pipe and radiation to for the heat to chase the cold.

No it does not. Increasing the flow rate of the system, would increase the average water temperature, which would increase the heat output of the emitters

Sylvain

@Doug_7
Ok, it seems I was wrong about running many zones with one pump.

Doug_7 said:

Do not over-estimate the theoretical energy dissipated by the valve.

About power necessary (energy by unit of time) ,
the pressure drop will vary with the square of the flow and the power necessary to drive the water through the valve will vary with the cube of the flow.
power= pressure drop X flow [easier in metric for me ;-) ]

1Cv valve > 1psi for 1 gpm; power: ( 6894.757 Pascal X (0.003785 m³ /60 s) = ~0.4359 W
1Cv valve > 9 psi for 3 gpm; power: ( [9 X 6894.757 Pascal] X ( [3 X 0.003785 m³] /60 s)= ~11.743 W
1Cv valve > 16 psi for 4 gpm; power: ~27.836 W

3Cv valve > 1 psi for 3gpm power: ~1.305 W

Doug_7 said:

Do add up the actual total pumping energy.

Right,if one has to restrict the flow without changing the delta P, the energy will indeed have to be dissipated anyway somewhere along the loop.


The OP question is a good one.

Cv is a way to have a bigger number for a bigger flow (for a given pressure drop) instead of a diminishing resistance number (commercial trick?).
Generally: delta P= K flow²
So if delta P=1, flow= Cv and then the resistance to flow Kv= 1/Cv² .
K of each component is added for components in serie to find the resulting K.
(as shown in the hot_rod spreadsheet calculation here above).

If delta P is the same for all the loops, the flow in each loop will be
loop_flow= sqrt(delta P/ resulting loop_K)
or loop_flow = resulting loop_Cv X sqrt(delta P)

So to halve the flow, one either divide Delta P by 4 or divide the resulting Cv by 2 (or other combinations).

farmwi

"Why are zone valves not full port" because the designer isn't paying for the cumulative power lost.

I switched to Belimo, ~full port ball valve, 75psi close of pressure, cv 1.4 on a 1/2" valve. imo best choice locally.
turned the pump down, and have better end to end temp stability from higher flow.

If restriction is needed wouldn't it be better to to do it separately adjustable.

hot_rod

farmwi said:

"Why are zone valves not full port" because the designer isn't paying for the cumulative power lost. I switched to Belimo, ~full port ball valve, 75psi close of pressure, cv 1.4 on a 1/2" valve. imo best choice locally. turned the pump down, and have better end to end temp stability from higher flow. If restriction is needed wouldn't it be better to to do it separately adjustable.

A full port 1/2” zone valve with a 1.4 cv sounds like an Oxymoron 

Here is the cv for typical ball valves. To make that ZV a low  cv it must be restricted to a 1/4” opening?

Doug_7

Sylvain - Not wrong - you just never heard of a system with that many zone valves supplied by a single pump !

This is a multi-family residential building with 21 suites - each suite is over 2,000 sq ft and has 8 or more zone-valves supplying in-floor heat - PEX in Gypcrete with Wirsbo Manifolds. Two 500 MBtu ModCons. Very cold climate (Canada).

Previous similar buildings have two recirculation pumps in each suite. That is a lot of extra pumps. Our new building heating system design, with one central supply pump, works like a charm (25 years experience). Very reliable and efficient.

I agree we should design systems to reduce all unnecessary flow-restrictions - they do waste energy. The total amount of energy they waste is ultimately measured by the total pumping energy. One pump drawing 120 watts while supplying a system with 170 zone-valves seems like pretty low pumping energy. Less than 6 watts per suite.

I never quite saw why we need to install so many pumps - like one per zone - to make a heating system work. Yes that will work - but why do you need so many pumps ?

High Water Quality is key to pump reliability and long-term life.


farmwi - Totally agree - If restriction is needed it would be best to to do it separately adjustable.

EBEBRATT-Ed

We had a building with 350 fan coil units and 1 pump. I think is was 12 stories high. They had 1 room on the 5th floor that had a computer room, so the pump had to run 24/7. I think the pump was 50 or 60 hp. There was no way to separate that unit from the existing mains.

To save energy we installed valves on the 350 fan coils and a vfd on the pump, now when all the offices were unoccupied and the fan coils off the pump backed down to only feed the computer room. Save a lot of energy.

MarkShean

adambuild said:

Simply curious: Why are zone valves not full port, but instead they have various CV restrictions? What is the reason / logic? Thanks in advance

taco sentry is full port and its a awesome zone valve.  the actuator isn't huge like someone else suggested it would be.  and it doesn't use much electricity 

hot_rod

taco sentry is full port and its a awesome zone valve. the actuator isn't huge like someone else suggested it would be. and it doesn't use much electricity


I guess we have different definitions of full port?

Here is the 1/2" valve you mention, the opening, orifice is about 19/64, just under 5/16"

Full port in the valve industry usually refers to a full sized open, as large as the pipe connecting to it. As in full port ball valves, etc.

I show it pulling about 1/2 amp as it charges the capacitor, then drops off.

farmwi

hot_rod said:

farmwi said:

"Why are zone valves not full port" because the designer isn't paying for the cumulative power lost.

I switched to Belimo, ~full port ball valve, 75psi close of pressure, cv 1.4 on a 1/2" valve. imo best choice locally.
turned the pump down, and have better end to end temp stability from higher flow.

If restriction is needed wouldn't it be better to to do it separately adjustable.

A full port 1/2” zone valve with a 1.4 cv sounds like an Oxymoron 

Here is the cv for typical ball valves. To make that ZV a low  cv it must be restricted to a 1/4” opening?

You are so right Bob "hot rod"! I just copied and pasted too quickly
I used a 3/4 in that looked like a ball valve to me, Belimo. So I looked up 3/4 it's 9.8cv. But I haven't looked in a long time. I was tired of 2 other brands failing over time. Online I could find more open ports. Here Belimo is rare. several of the brands I looked for were not stocked that I could find. Winter being cold enough that a couple days wait it too long for parts, used locally stocked parts.

Sootmaster

Wow, such a simple question can really blow up around here. 

hot_rod

farmwi said:

hot_rod said:

farmwi said:

"Why are zone valves not full port" because the designer isn't paying for the cumulative power lost.

I switched to Belimo, ~full port ball valve, 75psi close of pressure, cv 1.4 on a 1/2" valve. imo best choice locally.
turned the pump down, and have better end to end temp stability from higher flow.

If restriction is needed wouldn't it be better to to do it separately adjustable.

A full port 1/2” zone valve with a 1.4 cv sounds like an Oxymoron 

Here is the cv for typical ball valves. To make that ZV a low  cv it must be restricted to a 1/4” opening?

You are so right Bob "hot rod"! I just copied and pasted too quickly
I used a 3/4 in that looked like a ball valve to me, Belimo. So I looked up 3/4 it's 9.8cv. But I haven't looked in a long time. I was tired of 2 other brands failing over time. Online I could find more open ports. Here Belimo is rare. several of the brands I looked for were not stocked that I could find. Winter being cold enough that a couple days wait it too long for parts, used locally stocked parts.

Belimo tends to go more through control type suppliers than HVAC or plumbing channels. Supplyhouse.com, a sponsor here, has a selection of Belimo. I sometimes get stuff the next day from them.