why is using a differential bypass valve important with zone val

rb_6

Matt_40

why is using a differential bypass valve important with zone val

I recently went to a taco seminar. They briefly discussed using their diffential bypass valve with zone valve applications. Can someone help me understand why this is important and what would happen if i dont use this device. Would it be possible if only one zone was calling and say your pumping away would there be enough pressure built up to push a zone valve open that was'nt calling? Im a young plumber/heat tech if you cant tell all ready. I recently piped a boiler a using zone valves on the supply and pumping away from compression tank I still have the option to install the pressure differential valve. I got a price on it and it would cost $75 my boss is old school and never used them he still sticks the circ on the return I need to convince him as well as myself that this is important. Thanks for any imput. cheers

Joe Mattiello

Using a pressure differential by-pass valve will help keep the velocity consistent in all the zones. The pump is sized to handle all the zones calling for heat simultaneously because flow is collective, but if only one zone calls for heat the velocity can go up exponentially causing erosion, and noise.

clammy

differental pressure valves

Well coming here to learn is the greatest thing you could do for yourself and learning about the trade you have chosen ,hats off to you my friend , as for using a pdv with zone valves the main advantage is that it will allow your system circ to operate within it's pump curve and it also allows your pump to by pass part of it's discharge pressure back to the return side of your system which basically means that you are not over pumping a single zone when only one zone is calling which by over pumping means increased velocity in your supply piping which can translate into alot of smaller and larger promblems like velocity noises ,lack of proper heat transfer due to increased velocity ,air entrailing promblems ,fitting and pipe erriosion . By installing and properly setting a pdv you would get rid of those promblems and a few others like banging and hammering zone valves at the end of a call for heat due to the fact that most zone valve end switches do control your circ relay and the circ will run a couple of seconds before the relay opens and shuts the pump down ,dead heading pumps and wasted engery through your circ not run at it's rate pump curve .Even though these valves seem new to the US market (residental side ) they have been in use in europe for many years and most residental and commerical building heating system will have them ,they do things alot different over there in the subject of zone as to how we do things ,I believe there way of zoning and controlling heating systems is quite different then here there standards are a bit higher then ours with a higher install price but a much lower operating and fuel useage then ours .I am not saying that there is no one installing system like europeans have just that it's not something you will see everyday here and theer are those out there thats installs are equal or not better then the europeans .As for learning more about hydronics it's good to see you have come to the right place and just remenber that no one work up one day knowing it all it takes time and we are all human and are bound to make mistakes and hopefully we learn from it ,but just remenber to read and try to learn some thing from each old timer or one who may have more time in the trade and rene=meber that no ones knows it all we are ll still learning myself included big time peace and good luck clammy

Brad White_9

All the right reasons....

Matt, the other advice from Joe and Clammy is spot-on.

Your circulator can ride its curve only so much before it climbs to the high left side of things (no flow, all head, -sort of like a newborn baby except come to think of it they are all head have plenty of flow too-).

Anyway- here is another short-cut trick, not for complex systems but something I learned to use on lower cost systems where hot water flows in winter only:

If you have a kickspace heater or bathroom radiator or two, do not put zone valves on them. Just let the water flow throught as it may, perhaps with a good balancing valve but that is about it.

Baths never get warm enough IMHO and kickspace heaters or other fan-forced units can cycle their fans for capacity delivery when it counts. The idea is that these will act as the bypasses by default.

Absent that, I am a believer in the ideal: TRV's or zone valves on all emitters for local control and a good DP bypass valve (Macon, the Honeyewell D146, Oventrop among others) to bypass at a fixed differential.

Ken_40

If we continue

to use "cheap" wet-rotor circs. without considering the performance curves, we have little choice other than to istall DBP (differential by-passes.)

If we size zones properly, a flat curved circ., like the S-100, elimate the need of the DBP when one or all of the zones call.

Everyone seems bent of replacing or designing systems with small, straight-line performance curved circs., without regard to the resulting one vs. all zone calls for heat extremes.

We must not simply replace every "broken" S-100 with a one-fourth the cost wet rotor 007. It was a bad idea from jump street to do so, and continues to be the norm in this industry.

Issues that become problems with this mindset are:
1) Introducing air contamination - where none occured before
2) System noise - where none was present before
3) Insufficient heat when very cold outdoors, and
4) New circ. death from "frozen" rotors, jammed up by system crud being dis-lodged from dormancy, by higher velocities

Weezbo

it is a minor technicality...

think of it like this, seldom if ever does the field( all the zones in a system)match the exact size recirc that you can purchase.

so if i have a hundred gpm pump lets say and a small zone opens that pump cranks up and burns some energy to do that. in another time of the year all the zones close except a small zone,well,it cost to roll,the long term cost could easily be more than X dollars for the pressure differential by pass.the costs are hidden as it were,is there some things that could be done besides a pressure differential by pass that might be better? that is what you might ask yourself...and indeed there are.

the boss is not the problem, the operational costs can become the problem. most zones in a small home dont require a huge recirc that was simply an analogy ...often it is never even considered what additional costs may be incurred with the seasonal operation of a system. there are small details like pipe sizes for example that also add to the cost of operation, most people think

'ok you are the pro at this ,so,...i dont need to burn countless years of my life attempting to know everything you do about whatever it is you do just do whatever it is you do and get out of my life':) thing is we like what we do and like to do things to the best of our ability and knowledge. saving some dollars in the long run for someone else in a way puts a few more in your own.

there are products on the market that cost a few dollars to build and save lots of dollars.you depending on your age may see quite a few gizmoes in your life that are designed to improve financial comfort for the owners of one of the systems you design. if you want to know the truth i think there will be things in the future that will basically make a pressure differential by pass a faded memory:) your boss may have lived his entire life without even Seeing one:) so, in a way he may never be the wiser.nor will any of his customers. the cost to operate his systems is acceptable to his customers so neither of them particularly care that the pump isn't functioning in the ideal part of its pump curve 24/7.

Look under WILO Recirculation pumps for an example....spend some time reading the advantages of using one of their new residential P D recircs....

Ron Schroeder

Gee Brad

It took me fifteen years to figure out that I did the right thing by mistake. I installed a new boiler in Dads house and split it into 2 zones, where it was easyest to split up it left the bathroom on when either zone was calling. At the time I was counting on the fact that everyone likes a warm bath and it would not hurt to keep it that way. little was I thinking of a bypass go figure.

Bruce

Darin Cook_5

Pressure Differential Valves

PDV's are a band-aid to begin with. Like driving with your foot all the way on the gas pedal and pressing the brake at the same time to slow down. Just wait till the Delta P circulators arrive on our market at a reasonable cost. They will modulate up and down depending on load, always "sized" properly for current design conditions.








Darin