Orifice plates

SteveSteam

Orifice regulating plates are inserted in the valve unions of all the radiators to correct for (1) friction loss of pressure in the steam supply piping, (2) extra heat given off in exposed risers and other sources, (3) design errors in the amount or proportioning of radiation, and (4) the filling of radiators at uniform and even rates irrespective of size and location.

In the above statement, the number of the statement which is not correct is;

A) 3

B) 2

C) 4

D) 1

Can someone give me an answer and explain why?

jpf321

where did this question originate?

I'm fairly sure I know the answer, but knowing the context and origination of the question may firm up my thoughts. 

jpf321

the answer below ....

Being a smart SAT guy, I see that #1 is the oddball since it has nothing to do with radiation.



Being a smart STEAM guy, I know that

  #4 is true since I have spent many hours drilling orifices for exactly this purpose

  #2 is true although orifices are always drilled for exsiting radiation and OVER RADIATION is handled differently .. you can always decrease an orifice size to limit heat to a rad, but you can never fix an UNDER RADIATION problem

  #3 is true for the same reason as #2. You can use an orifice to fix an OVER RADIATION situation .. but the reverse is not true.



For your own clarity .. an orifice is exactly the same as a 1-pipe air valve .. except you can't use orifices in 1-pipe can you?

  #2 and #3 .. you can limit heat to a rad by decreasing it's vent size .. (#2 fireplace in the room perhaps) (#3 south facing well insulated new triple pane windows room right over boiler room with a 100sq ft EDR radiator)

  #4 .. you hear all the time of balancing systems by altering rad venting .. the bigger and further from the main the rad .. the larger the vent .. small close rads get small vents.



I hope this helps .. How'd I do? Where did this question come from? Send us more.

jpf321

you may want to ...

Look up a paper by D.E. Schroeder written in the 40's called "Balancing a Steam Heating System by the Use of Orifices" if you want more information. 

jpf321

Lastly .. from ASHRAE 2008 Chpt 10...

Dave in QCA

my answer is

All of the statements are true.

gerry gill

my answer is

None of the remarks are COMPLETELY true without the famous 'it depends' attached..orifices are use to balance..but the orifice size is not uniform from radiator to radiator..location, size, venting proximity, all play a role in how big the orifice hole is going to be..with the eventual goal of uniform room temperature from room to room..just my 2 cents.

jpf321

i think the question implied...

that there would be variations in orifice sizing .. the question was rather ..



Can an orifice be used to correct for frictional losses?

Can an orifice be used to correct for external heat sources/considerations?

Can an orifice be used to correct for disproportionate room radiation?

Can an orifice be used to balance steam arrival timing?



I believe that the last three can be answered YES while the first one is a NO.

The Steam Whisperer (Formerly Boilerpro)

Yes, all are true

The first is also sometimes covered by installing plates in the supply mains.  This is discussed in manufacturer's literature from at least the 1940's.  The rest cover a variety of heating imbalance possibilities which plates can be used for.

jpf321

very cool ...

I didn't realize that one would want to correct the friction losses nor that orifices could accomplish that. Thanks BP for the lesson. I suppose the test makers (although at this point, we will perhaps never hear from the original poster about where this question came from) didn't realize it either. 

Dave in QCA

All are true and none are true

As Gerry says, it all depends.

First, to make the case that none are true, one would have to consider operating conditions different from what we usually see.  In residential steam, we usually see intermittent presence of steam.  In the old days, people would refer to whether the steam was "up" or not.  In the process of steam coming up, we usually see partial steaming.  That is, the boiler will fire, steam will start to travel, the radiators will partially heat, no pressure will be built, boiler shuts off.  These are the conditions that orifices make a huge difference. 



But what are the conditions where an orifice will make no difference.  Let's assume that the orifice for a given radiator is sized to fully heat the radiator at 2 psi.  Let's assume that the boiler is firing and steam is up.  The system is fully heated and pressure has built to 2 psi.  The boiler is cycling off and on and maintaining 2 psi. Let's also assume that this is a constant state and will continue to operate this way indefinitely.  The radiator and the entire system is fully heated and all radiators are putting out their max.  You remove the orifices and the system will still perform exactly the same way.  Thus in this scenario, none of the questions posed are true.   In this constant state scenario, the orifice can be sized to match the EDR of the radiator and therefore eliminate the need for a trap.  We can create a situation where question #2 & 3 are correct if we are under-sizing an orifice to reduce the amount of steam entering a radiator.  The orifice can be sized smaller than the EDR, and effectively reduce the heat output of the radiator, but it can't be over-sized to increase the output.  But since the steam conditions in the main are the same in both cases, the orifice will have no effect on the arrival time, (steam is always there) and it will have no effect in compensating for pressure drop because there is no difference created in the main as a result of the orifice.



But this isn't the way most residential systems operate and so we need to consider the conditions that actually exist in most residential steam systems.



Carefully note the comments by Dunham in the their advertisement for "regulating plates", the term they used for inlet orifices.  Image posted below.

 

The conditions where orifices are most effective are when steam is not always present, and where the steam cycles only partially fill the radiators.  First let's pick a pressure to which we will size the orifices.  I used 8 oz in my system.  It can run at lower pressures and partially fill the radiators under constant steam, or at higher pressures of 10-12 oz, the rads will be filled quicker, and since I have working steam traps, over supplying the radiator is not a concern.  Henry Gifford prescribes 2 psi as a good operating  pressure for an orifice system because the effects of pressure drop in the piping is minimized, so let's use 2 psi for discussion. 



In a partial steaming condition,  which is probably the vast majority of heating cycles.  When the boiler first starts to steam, we may see 1 to 2 oz of pressure at the boiler.  The steam will work its way down the mains, expelling the air at the vents.  Steam travel into the laterals and risers will be quite slow and at about the time that steam reaches the main vents and they begin to close, steam will also arrive at the radiator.  It might arrive a bit before, but even so, the flow into the the radiator through the orifice will be so slow that no warming of the radiator will likely be felt.



Then the main vents close and the action starts.  The pressure in the main will quickly begin to rise, and as it does so steam will begin to enter every radiator.  The flow rate will increase as the pressure increases until the pressure reaches 2 psi.  If the boiler is over sized, it will cycle off and on to maintain a 2 psi average.  If the boiler is closely sized to the  load, it will fire continuously and everything will be in equilibrium. 

 

Fifteen minutes later, the thermostat is satisfied, and the boiler shuts down.  If the orifices were sized for the actual EDR of the radiator (let's pick 40 sq ft, it will probably be heated about 25% of the way (10 sq ft).  If the orifice was under sized, say for 30 sq ft, the radiator will be heated to about 25% of 30 sq ft (7.5 sq ft).  If the orifice was over sized, because the room is usually too cool, let's say the orifice is sized for 60 sq ft, then the radiator will have been heated 25% of 60 sq ft (15 sq ft).   In this manner, individual orifices can be adjusted to both decrease and increase the effective EDR of a given radiator.  Even in a long cycle where full saturation of the radiator occurs, while the oversizing effect will be decreased, it will still have some effect because the over sized orifice will cause the radiator to come up to full temperature faster the the other radiators and it's effective heat output over time will be greater per actual rated EDR than the other radiators in the system.  I believe it was Dave Bunnell who referred to this ability modifying radiator output as the "virtual radiator".



So, we've now covered questions 2, 3, & 4.  What about #1 and frictional pipe losses?  Frictional pipe losses at very low pressures, say 1-2 oz are quite large and are at the root of distribution problems.  Every elbow, tee, or length of pipe, and even turbulence within the pipe causes some resistance to flow.  At 2 oz of pressure, the pressure drop is so small that it would be difficult to measure, but as a percentage of the pressure, it is quite high.  Raising the pressure in the main will decrease the pressure drop.  According to information at http://www.engineeringtoolbox.com/steam-pressure-drop-calculator-d_1093.html   



When considering a 100 meter length of pipe, increasing the pressure by a factor of ten will decrease the pressure drop by a factor of 10.  Thus, the pressure drops that are present in the piping during the steaming cycle at 2 oz. in a non orifice system  will be greatly reduced by the addition of orifices, which causes the pressure in the mains to be raised, in this case to 32 oz (2psi), which is a factor of 16.  This is in part the reason that orifices are able to equalize the distribution, the various pressure drops that occur all throughout the steam mains are effectively removed from the equation.