Circ pumps vs z valves

Mike T., Swampeast MO

Once you have the ability to control heat authority via your proportional flow control, you can manipulate systems and sub-systems for the most efficient (lowest) heat authority <I>allowing expected response</I> in a space of differing construction methods and occupant desire.

Dm_3

zone valves vs circ pumps

Can someone please tell me if using circ pumps on a two zone system with an indirect water tank is more efficient than using zone valves and also why is it better I'm told to set up pumps on supply side rather than return side.

Rod Kotiga

Pumping Away

I like pumps for the simple fact that if your main pump goes down in a zone valve system you have no heat leaving your boiler as opposed to a pump system you'll still be able to deliver heat to other parts of the house. As far as pumping, always on the supply side and downstream from the main air vent and the expansion tank. As far as why in short, you could start sucking air into your system which in the long run can result in a lot of oxygen corrosion in your system. You might pick up little known book called " PUMPING AWAY " by some guy called Dan Holohan ( ha ha). Don't worry you don't have to be a graduate of M.I.T. or come from the planet SMART FIVE to understand it. It's written in a way that you don't have to whip out a dictionary every other sentence or a calculator. Those books come later if your into figuring exactly how many droplets of water your system will need and the exactly how many watts of power your using.

Rod

Dave Holdorf_2

Ahhhh, Pumps vs. Zone Valves

Rod-

I used to agree with you about zoning with pumps. I designed alot of systems that way many years ago. However, the times are a changin'.
Lets take a scenario; if a pump goes down in a system, how hard is it to get a new one installed on the project. Do most service people have on their trucks for just that occasion? Will the serviceman be able to get to a wholesaler easy enough and get a new one (how many skids of pumps do most wholesalers have in stock?). And if they are closed, don't some of them have some special phone numbers so that the serviceman can get something after hours?

When you stop and think about it, a zone valve system may be the better system because of the electrical consumption of the system. With more and more sophisticated systems, multiple zones, outdoor reset......we should try and minimize the high voltage components being used.

We are designing and installing energy efficient power plants, we need to also look at the amount of electricity is being consumed by these systems. We should also analyze the Watts per BTU for making the best possible systems for our customers.

So in summary it does depend on the pump requirements for the load, but I have started designing with alot more zone valves and actuators on projects the last few years.

realolman

Why

would the pump being located on the return side cause it to suck air more than on the supply side?

Also, if the manufacturer's manual calls for the pump to be located on the return side, isn't that where an installer is supposed to install it?

Mike T., Swampeast MO

When the pump circulates towards the expansion tank connection (PONPC), it can only do so by reducing pressure at its' inlet. In high head (or all-too-common overpump) situations, the inlet pressure can drop to sub-atmospheric thus having the ability to literally suck air.

PONPC = Point of No Pressure Change

Larry C_13

Pumps provide a DIFFERENTIAL pressure.

Pumps provide a DIFFERENTIAL pressure. For example, lets say the circulator in your system will provide a 20 psi difference between its suction and its discharge.

Where the expansion tank connects to the system piping, the gauge pressure (pressure that is referenced to atmosphere)won't change as the system heats up or cools down. (That is the purpose of the expansion tank.)

If the pump suction is connected at the expansion tank port, the pressure at the discharge of the pump is expansion tank pressure PLUS 20 psi. At the inlet to the boiler, the pressure will be a couple of psi above the expansion tank inlet. Which is the same as 18 psi below the pump dischage pressure.

Now move the pump to the inlet of the boiler. The discharge pressure of the pump will still be a couple of psi above the expansion tank inlet pressure. The pump suction will still be 20 psi less than the discharge pressure.

Now lets plug in some numbers. Expansion tank inlet pressure equals 15 psig. Remember this pressure does not change. Pressure across the pump is a constant 20 psi when the pump is running. Pressure drop across the boiler is 2 psi.

Pump suction connected to expansion tank.
Expansion tank pressure = 15 psig.
Pump suction pressure = 15 psig.
Pump dischage pressure = 35 psig. (15 + 20)
Boiler inlet pressure = 17 psig.
Boiler outlet pressure = 15 psig.

Pump discharge connected to boiler inlet.
Expansion tank pressure = 15 psig.
Boiler outlet pressure = 15 psig.
Boiler inlet pressure = 17 psig.
Pump dischage pressure = 17 psig.
Pump suction pressure = -3 psig. (17-20 = -3)

That means the suction of the pump is less than atmospheric pressure. If air can get into the system at the pump, there is a 3 psi pressure difference pushing air into the system. Air will come in!

More air leads to more oxygen, which leads to more rust, and earlier failure of steel components.

Mike T., Swampeast MO

Sorry--forgot to mention manufacturer's manuals...

For most conventional residential boilers there's no reason not to pump away regardless of where any included circulator is attached or the "typical system" illustrations in the manual. When a circulator is not included, you'll find that most will illustrate "pumping away" in their manuals. You stand to gain high benefit at almost no additional cost. (Even with copper sky high a few feet of BX is cheap.)

For mod-cons, the situation is VERY different with many manufacturers specifically and only showing pumping towards the PONPC.

With mod-cons, the heat exchanger itself is the prime restriction in the system--the "only" restriction if primary-secondary. The heat exchangers are also able to deliver heat very rapidly.

If the circulator pumps away from the PONPC it will add to the fill pressure seen by the boiler's safeties. Should load suddenly drop with the burner at high output, system pressure could momentarily rise above limit before burner output is reduced. By pumping towards the PONPC into an HX of known, and predominate resistance, the boiler sees nothing higher than static pressure and as long as mfgr. piping and circulator selection instructions are followed there will be no chance of approaching sub-atmospheric pressure.

As a group, the heat exchangers used in mod-cons have very high resistance to flow. The Triange Prestige is the standout with a uniquely flowing HX design that maintains transfer efficiency at relatively low velocity by guiding laminar boundaries towards the path of their own destruction.

Robert O'Brien

Invest

$30 and sign up for this webinar.I love the hammer analogy!
Robert Bean's Zoned - Valves vs Circulators...

When you can control the flow you have authority of the system. Having authority of the hydraulics allows you to effectively use temperature modulation to match the load. Robert Bean's Zoned Valves Versus Zoned Circulators explains why valves or circulators are tools to reach this objective. Avoid the "have hammer in hand - everything looks like a nail" syndrome.This is an 80-minute presentation.
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realolman

So

you're saying that if I hook up a gauge as pictured in the attatched drawings, I will get a lower pressure on the gauge than the expansion tank pressure, and possibly even a vacuum if the pump is hooked to the return side of the boiler ?

And it will be higher than expansion tank pressure if the pump is on the supply side?

I ain't from Missouri, but I am hard headed. I have my boiler down for some modifications now. You can bet I'll be checkin' that out.

Mike T., Swampeast MO

Yes, that's exactly what I'm saying and I am from MO. Dan Holohan explains the LAW that GUARANTEES such behavior simply perfectly in Pumping Away.

Unless this is a gravity conversion system (HUGE PIPES), you should DEFINITELY switch to "pumping away" with a conventional boiler "down for some modifications". Such is simply and ideally shown in SUPPLY.JPG

CC.Rob_7

all of which reminds me...

to ask what's up with the Wilo ECO series? Are they available in a standard US 115V, "standard US" flange configuration yet?

Tom Kane

Wilo Stratos Eco

Yes it is available......ask your favorite distributor to contact their Wilo Rep and they should be able to get details very easily

Mark Hunt_6

\"They're here\"


Yes. The ECO has landed. 115v or 240v, take your pick.

All "North Americanized" flange configurations and head settings.

Bronze or Cast Iron bodies.

We are currently filling back orders so if you want one.............or twelve.......let me know. (I got people)

Mark H

Rod Kotiga

pumps vs zone valves

I agree on the electrical consumption side of zone valves vs pumps. More so now that Wilo has come out with the Stratos Eco.

Rod