Head And GPM

Larry_10

hi can someone please tell me what head room is and what it's used for?

and how do you know what the delta-t's will be when you put a system together

I am just trying to understand the terminology

thanks

Mike T., Swampeast MO

"Head" is a measure of resistance to the flow of water.

Tables are available for computing loss in piping and fittings of various sizes and material. For other components (like the boiler, radiation, zone valves, check valves, etc.) use data from the manufacturer. If a single circulator is serving multiple loops the head loss is the greatest encoutered in any SINGLE loop--not the sum of all of the loops!

"Headroom" is the difference between what is available and what is being currently used. It has nothing to do with friction loss.

"How do you know what the delta-ts will be when you put a system together?" Great question but I can't answer. When sizing a system we make assumptions regarding delta-t--VERY frequently 20° because it makes the math easy... Fortunately it seems to work reasonably well in most cases even if the actual and assumed are frequently substantially different.

Larry_10

so if my delta-t's are 20deg different then my head and flow rate are ok and the pump size is good. right

if my delta t-s are 30 to 40 then I need a bigger pump because the head room is to big? right

how can I tell how many gpm my baseboard's need and use

I have 44 feet of baseboard installed on one side of my house.

is each 90 used in the loop a restriction how do you measure how much restriction will be in a loop do you count how many bends are in the loop like 90's and 45's?

im trying to understand this I am going to school for HVAC next year I just want a nice head start :-) so im the smart one in my class :-)

thanks

Mike T., Swampeast MO

so if my delta-t's are 20deg different then my head and flow rate are ok and the pump size is good. right

Yes.

if my delta t-s are 30 to 40 then I need a bigger pump because the head room is to big? right

Maybe yes, maybe no. Presume you're talking about fin baseboard installed in a series loop here. While 40° delta-t is pretty high, you can design the loop for any reasonable delta-t (believe that 30° is the generally accepted max). There is a DEFINITE limit on the flow through a loop--generally around 4 gpm for a ¾" baseboard loop. A very high delta-t can well mean there is too much baseboard--just adding a bigger pump ain't gonna' help! Also remember that when designing you're making a delta-t ESTIMATE--in actual operation things are likely to be VERY different--particularly as the weather changes.

how can I tell how many gpm my baseboard's need and use

It all depends on how much baseboard is installed and the supply temperature used. Manufacturers of baseboard, panels and other heating devices often have very good literature available on-line regarding how to use and size systems using their materials. There are also many books (old and new) available.

is each 90 used in the loop a restriction how do you measure how much restriction will be in a loop do you count how many bends are in the loop like 90's and 45's?

Each and every fitting offers restriction to flow. The amount of restriction varies based on the amount of flow--the higher the flow the greater the restriction. Tables are available on the web and in books. Restriction in the pipe is based on loss per 100'; restriction in fittings is per each and per type and is given as an equivalent number of feet of straight pipe.

Larry_10

mike your the man thanks very much :-) i love this stuff

Empire_2

Mike

GOOD EXPLANATION....:) Also, To New Student.... as you get into the field,...There are very useful tools such as the B&G's Cystem syzer Claculatior which you can obtain if your A Pro., or a student from B&G. This invaluable tool will give you, explanation and answer your questions provided that you have a ballanced knowledge of what you need to know to solve the problem. Mike and Weezbo are very knowledgeable in the field and I'm sure that they can steer you in the right direction with all your questions.. Most important,..... Have facts,,measurements and descriptions so you can be helped.

Kal Row

you can buy siggi's software at hydronicpros.com...

and then you can play with pumps/lenghts/sizes/fitings until you are blue in the face and watch the software calculate it for you (see siggi.jpg)

his book and software together is the best deal - here is the link (copy it all in one shot)


http://sf1000.registeredsite.com/~user929996/miva/merchant.mv?Screen=PROD&Return_Screen=LIST&Store_Code=HE&Product_Code=HDSMHH2


this free plug, is my way of paying him back for all those wonderfull articals in PM magazine