Zone valves and volume

larryjbjr

Ok, I am a homeowner trying to do my own heating work. I have an older 2 story home and I want to hook up 2 zones, one for ground floor and one for upstairs. So, I went to Menards to get a couple zone valves, but when I looked at them I see that even though they are 3/4" sweat connectors, with the valve inside the opening is more like 1/2 inch so.

My question is this, if a 3/4" line can carry 40, 000 or so BTUs of heat, will this zone valve, by the way the valve restricts the flow, reduce the heating capacity? Or , will it still allow the full volume of water as the 3/4' pex?

larryjbjr

Ooops, I think I posted this in the wrong section. I meant to put this in Radiant Professionals.....

Jamie Hall

No problem. It will affect the head the pump has to work against, but the effect is small.

Paul S_3

@larryjbjr .... do not worry about flowing 40,000 btus through that valve....i believe it has to do with the Cv value which is 3.5 for a Honeywell zone valve....so you can flow 3.5 gpm through the valve at a 1psi pressure drop...someone correct me if im wrong not a 100% on Cv value....just be more concerned with proper distribution piping, loop length and using the correct pump ....if your using 3/4" fin tube baseboard do not go over 65ft of element for that zone...if you have to jist split the zone

larryjbjr

Ok, so what about the couplings and such that I connect the pex tubing with? For instance, if I use 3/4" pex, and connect it with brass couplings and such, the actual inside diameter of the brass coupling is more like 5/8". Someone told me that, when I do that it basically reduces the whole line to whatever the inside diameter of the brass coupling is. So, basically, the coupling is a bottleneck....

So, is that not correct either?

larryjbjr

And, would you kindly explain what you mean by the head the pump has to work against?

Paul S_3

Yes .... 3/4 pex is a little more restrictive...dont go piping in 30 pex elbows in a zone...how big is the area you want to heat(sq ft)? How much fin tube are you using ? What kind of pump are you using? Maybe someone else can explain pump head to you alot better than me...basically every component in the loop elbow, tee, valve etc equals to a length of straight piping....you would add all the components together plus the straight piping that will give you your "total equivalent lenghth" then i believe you multiply it by .04 that will give you a rough estimate....i usually use computer software for larger jobs....Caleffi idronics explains it alot better

Paul S_3

http://www.caleffi.com/usa/en-us/technical-magazine. ......read #16 circulation in hydronic systems

Jamie Hall

larryjbjr said:

And, would you kindly explain what you mean by the head the pump has to work against?

In any piping system there are losses due to friction an other sources -- such as those valves (minor) and all the elbows (which may not be so minor) plus the pipe itself. Those losses are related to the flow. The pump must create enough pressure -- which is also called head -- to equal those losses at whatever flow you may have. More flow, more pressure required.

delta T

Pumps move water by creating a pressure differential between their inlet and the outlet. Every system has a 'system curve' and every pump has a 'pump curve'. What the pump curve tells you, is what pressure (head) the pump can create, and what the flow rate will be at that pressure, across the entire operating range of the pump. A system curve tells you how much pressure drop (pressure drop and head loss are the same thing) the water will experience as it circulates in relation to a desired flow rate. Head increases exponentially as flow increases (a 3 fold increase in flow will result in a 9 fold increase in head for the same system). On any given system, where the pump curve intersects the system curve you will have the true operating point of the system.

The best way to think about about it, is that pressure that the pump adds (by creating its pressure differential) is subtracted by friction. This friction develops as the water flows through piping, valves, 90's, anything at all really. This friction manifests itself as pressure loss. If you put a pressure gauge every foot throughout the entire circuit, you could see the pressure successively drop as you followed the circuit around, with the highest pressure being at the outlet of the pump, and the lowest pressure being at the inlet. The amount of this drop depends on how much friction is generated. The friction depends on the flow rate (faster flow=more friction) and how many things (piping, valves, etc.) the water is in contact with over the course of the circuit and how restrictive those things are.

Agree with Paul S, that Caleffi journal he linked to, will explain it in great detail if you are interested.

@Paul S yes, the standard 3/4 honeywell ZV has a CV of 3.5, the bigger ones have a CV of 7 or 8 (can't remember for sure, but had one of the 3.5 ones on the shelf)

To the original question, I sincerely doubt you will have any issue with that zone valve. If you are curious, 1 PSI = 2.31 ft of head.

larryjbjr

Ok, thanks to all of you for the great information. First of all, the more I read, the more I realize I don't know. I thought the more hot water I could send to my heaters the better. Obviously I was dead wrong.

I have a 2000 sq ft 2 story home (1400 sq ft ground floor and 600 sq ft 2nd floor) with a full basement. My boiler is a Burnham, about 28 years old, putting out 107,000 BTUs. I have 5 cast iron radiators, 2 10,000 btu kick space heaters, and about 28' of baseboard heaters. But, my boiler, which is set at 190 deg, can run for an hour and my radiators never go over about 140 deg and the baseboards never get more than a little warm

By the way, I'm about an hour north of Milwaukee, WI.

So, I just recently bought a new circulation pump for my system, I thought the old one was way insufficient. It only did 17gpm, and 15 ft of head (I thought head was how high it would push the water) Since I am feeding the 2nd floor with 2 feeds from the basement, I thought that I needed more head I bought the most expensive one Menards had that would push 40 gpm and 33 ft of head

Anyhow, from what y'all are saying, that 15 ft of head has nothing to do with how high it will push the water, huh?

So, I'm probably over powering my heating system then?

Harvey Ramer

Sounds like you have a large mining pump that you can hopefully return.

I'm pulling these numbers from the back of my head, but I believe a pex 90 is equivalent to 11' of straight pipe. A tee, flowing out the branch is equivalent to 13' of straight pipe. A copper 90 is equal to approximately 2' of straight pipe.

Paul S_3

Its a closed loop system height has nothing to do with head just the total equivalent loop length...a 100 ft loop running horizontally would have the same head loss if it ran vertically....the weight of the water coming down will pull the water up all the circulator has to do is circulate (create a pressure differential ) to move water...kind of like a ferris wheel...the circulator being the motor and the carts being the water in the loop....your pump is huge you dont need that much pump @larryjbjr

larryjbjr

Harvey Ramer said:

I'm pulling these numbers from the back of my head, but I believe a pex 90 is equivalent to 11' of straight pipe. A tee, flowing out the branch is equivalent to 13' of straight pipe. A copper 90 is equal to approximately 2' of straight pipe.

1. Does this apply to all pex sizes, or does the pex size matter?
2. When determining head, do you count the run length including the return, or just the feed?
3. If my pump says Max Head: 33.1 feet, does that mean total for all runs, or just for the longest run?

Be patient with me, I think I'm starting to get the picture. I will give you what I think are the answers

1. Yes, for all pex sizes
2. You would count the entire run from pump to emitter, and back to pump.
3. Total for all runs should not exceed Max Head.

How am I doing?

Jamie Hall

On your number 3 -- if the runs are piped in parallel -- that is, the water can go to this one or that one, without having to go through them sequentially -- then the required head is the friction loss for the longest run, not the total.

Where it starts to get interesting is that the flow will divide between the various loops so that each one has the same friction loss (remember -- friction loss varies more or less with the square of the flow). So a short loop will get more flow -- sometimes much more flow -- than a longer loop.

So -- if you have a system with some short loops and some long loops, you may have to introduce some additional friction loss -- with a partially closed valve -- in the shorter loops to persuade the water to go through the longer loop. That's called balancing.

NY_Rob

Remember to use only oxygen barrier PEX for closed loop hydronic heating. The rolls/sections sold at the big box stores are not OB PEX unless specifically printed on the pipe.

Zman

When you say "my boiler, which is set at 190 deg, can run for an hour and my radiators never go over about 140 deg and the baseboards never get more than a little warm" do you mean it is firing continuously or is the burner cycling on and off.

With those cast iron radiators, you may have more of a thermal equilibrium issue than flow issue. If the radiators significantly outsize the boiler, you will never get to the set temperature. This may or may not be an issue depending on how your system is setup.

Details and pictures would help.

larryjbjr

NY_Rob said:

Remember to use only oxygen barrier PEX for closed loop hydronic heating. The rolls/sections sold at the big box stores are not OB PEX unless specifically printed on the pipe.

Unfortunately, I used mostly standard PEX. I was recently told I should have used OB, so I'm gonna have to change it out. I can't afford to do so all at once though, so I'm gonna have to do it a little at a time.

larryjbjr

@Zman

I "think" the furnace is constantly cycling. But, not sure about that. I'm gonna have to watch that more closely.

Here are pictures of the radiators I have set up. I don't think they are outsizing the boiler. But, what do you think?

Zman

I think the radiators are massive and the boiler will never reach the set temp. They will still heat the house although if the other emitters are sized for the higher temp, that is not good for even heating.

Another issue that comes with the low temps is boiler condensation. If you have a non condensing boiler, you are probably damaging it with low return temps.

Pex installations come out much cleaner if you hard pipe though the floor before converting to pex.

NY_Rob

3/4" OB PEX "A" grade...
http://www.supplyhouse.com/Mr-PEX-1240010-3-4-Mr-PEX-Oxygen-Barrier-PEX-Tubing-100-ft-coil

larryjbjr

Ok, I don't understand.

I looked up the radiator in the 3rd picture, and it is rated at 9000 btu. So, based upon that I guestimated the other radiators and came out with a total of less than 40,000 btu for all of them together.

I could be off by a bit, but my boiler is rated at 107,000, though after 22 years it may be less than that by now. So, even if it's only 80,000 btu then I should be fine.

Again, if I'm wrong please tell me and I'll do what I need to to fix the problem.

Here is the label on my boiler.

Zman

I am following your thinking. Perhaps that is not whats going on.
Take look at your boiler and watch the temps and the cycles.

Jamie Hall

There are several factors going on with your nice cool radiators. Unfortunately, from the descriptions I can't really say what's what.

However, the first thing to consider is that the heat delivered in a given situation may be found from the standard hydronic formual: BTU = flow (GPM) times Delta T times 500.

Second, the heat given off by a given radiator is related to the temperature of the radiator: for steam, it is 240 BTU per square foot, so knowing the EDR (area) one can get the heat given off by the radiator. For hot water, the heat given off is much less, due to the lower temperature -- someone has the formula for it, but I don't right to hand.

Now if the radiation can't absorb all the heat from the boiler, the return temperature will rise and the boiler will cycle off.

If you want to get more heat out of a radiator, you have to increase the temperature of the radiator -- either decrease the delta T (more flow) or increase the input temperature.

Those radiators you have are huge. However to find out what is really happening, you have to have the temperature of the water going to the radiators (not what the boiler is set at, what it really is), the temperature coming back, and the flow rate.

If your boiler is shutting off on high limit, you need more flow, given the temperatures you are quoting.

larryjbjr

Jamie Hall said:

Those radiators you have are huge. However to find out what is really happening, you have to have the temperature of the water going to the radiators (not what the boiler is set at, what it really is), the temperature coming back, and the flow rate.

Ok, is there a way to do that without unhooking the radiator, putting a guage on either end and hooking it back up?

I may be wrong, but I don't think it's too little flow. As I said above, I have a way over rated pump for my system. I think I'm more likely to have too much flow than too little flow...

So, do you think the radiators are huge compared to my boiler rated output? I've got 2000 sq ft to heat, and it seems like don't have enough emitter, not too much. Unless you are saying that it's better to have several small radiators rather than a few bigger ones.

I've got the heat on now. I'm watching it to see if the boiler is short cycling or not. But, so far I don't think so.

As always, if I'm wrong, just tell me.

Jamie Hall

An IR thermometer is your friend. Wrap a layer of electrical tape (black) around both the inlet and the outlet and use the thermometer to measure the temperature of that. It will read pretty closely. Do the same for the boiler -- inlet and outlet.

larryjbjr

Just a quick note. I just checked my boiler, and after running about 25 minutes the water temp is showing about 155 deg.

I do have an IR thermometer, and just used it.

Now, I checked the 1.25" copper return pipe going back into the boiler and it shows around 132 deg with the IR therm.

So, based upon that, I have a delta temp of 23 deg, and I have my pump set at the lowest setting, which is 23.7gpm. Using the above formula, I am putting 272, 000 btu in my house. Now, I know that ain't right. So, what am I doing wrong? Calculation wise, I mean.

larryjbjr

Just did it again with the black tape trick on both ends of the boiler. It's about a 10 delta temp.

So again, if my pump it putting out 23. 7gpm, that's still 118,500 btu. So, what's the deal? Now, assuming the delta temp is only 8 deg, then I'm right on. If my pump is flowing 23.7 gpm.

Is it possible that my pump is not pumping the full 23.7 gpm since I have several of the valves partially closed to try to restrict some flow to emitters?

Jamie Hall

Very possible. Very likely, in fact. Every pump has a characteristic curve of how flow it can mange for a given head, and if you increase the head, the flow can drop -- sometimes rather dramatically.

bob_46

Is that an upside down steam trap on the radiator with the valve?
Do you have air bleeder valves on both radiators?
In my opinion there is no way you are moving 23 gpm through your system.

Zman

I agree with Jamie on your flow estimate. 23.7 is a total SWAG with your combination of piping. One way to get a more realistic number would be to measure the pressure on either side of the circulator and plot that on the pump curve. Assuming your boiler is firing at design spec, it may be easiest to estimate based on delta T.

In any event, does the boiler ever get above 140 on the return? It really needs to finish every call for heat with a hot flue to prevent condensate damage. There are piping options to prevent this damage.

How long did the cycle you where monitoring last? What were the temps?

How do the spaces with the radiators heat? From a heating point of view, there is no reason the rads need to get to 180. If the space is being heated, lower temps are fine.

larryjbjr

bob said:

Is that an upside down steam trap on the radiator with the valve?
Do you have air bleeder valves on both radiators?
In my opinion there is no way you are moving 23 gpm through your system.

Is that what that is? I thought it was just a valve. Does it need to be right side up?

I have air bleeders on all radiators but that one. I tried removing the plug to put on in, but it's way too tight.

bob_46

Take the trap off and throw it. You must have a way to get the air out of the radiator.

larryjbjr

Zman said:

In any event, does the boiler ever get above 140 on the return? It really needs to finish every call for heat with a hot flue to prevent condensate damage. There are piping options to prevent this damage.

How long did the cycle you where monitoring last? What were the temps?

How do the spaces with the radiators heat? From a heating point of view, there is no reason the rads need to get to 180. If the space is being heated, lower temps are fine.

Yes, the last run was an hour, and the water temp reached 180 just at the end. And, I checked the return temp a while before that, when the supply was 160, and the return temp was like 150.

Well, I have my thermostat set to turn on at 68 and off at 70, and this last run took an hour to raise the temp two degrees, with 26 deg outside with 20 mph wind out of the West. So, the space is heating, but slowly.

I will give some room that maybe I'm just expecting too much. I just moved to WI from Los Angeles, and this is my first home I ever owned, and my first experience with Hydronic heat.

larryjbjr

bob said:

Take the trap off and throw it. You must have a way to get the air out of the radiator.

Ok, I'll do that.

That's why I have the inlet on the bottom and the outlet on the top, to bleed the air out. What I did when I first turned it on, was disconnect the return and stick it out the window, then once the air was out I connected it up.

Zman

Nothing wrong with 2 degrees an hour....

larryjbjr

Zman said:

Nothing wrong with 2 degrees an hour....

Really? That seems like a long time to me....

So, am I just on a wild goose chase then?

Zman

Some folks like to have systems that can change temperatures very quickly. Most do it because they think they will save energy by turning down the temp.
I like to think of it like highway vs city driving.
Which is more fuel efficient? A Prius cruzing along at 60mph or a Corvette trying to break a 0-60 record?

larryjbjr

I just figured if I could cut down on how long the system runs I would save money.

Just seemed to be running too long.

KC_Jones

In a perfect world it never stops running. That means you are putting in exactly what you are losing.

Gordy

That blue pex is NOT O2 barrier pex. is the rest of the pex barrier pex? This will let oxygen in the system. Not good. So while you are running around with the IR gun check each rad supply, and return temps. good time to balance the system.

In your case you have a lot of mass in the rads, probably a less efficient r valued envelope, and trying to bump up 2 degrees from set point. Tighten up the thermostat setting to .5 to 1 degree differential from desired set point. Then see how long the boiler runs to hit set point.


Right now you say it took 1 hour to gain 2 degrees.
However how long to the next call to satisfy the t stat? 2 hours 3?

Divide the 107 k (the 1 hour the boiler ran) by the time it takes till the next heat call that will be your btu input per hour.

If the boiler ran for 1 hour, and did not for the next 2 hours after that cycle then the envelope required 35600 btus per hour. that is if the boiler is tuned to 82% efficiency of course.