Head Question?

Ronbo

I am running four zones(loops) 3/4 copper off my main 1 1/2 header. I currently have them all running off one thermostat. When it calls for heat all the zone valves open at the same time. Do I still only calculate the head for my pump from the longest of these loops or because they open at the same time(all the time) do I add them together? Ty for any help.

icesailor

Zone heads:

Why on earth would you have all four zones and valves running off one thermostat? 

If you are doing as you say, the "head" is the entire system, with all the zone valves open amd the circulator running.

IMO, that is only your theoretical head pressure through the system. The "true" head pressure is measured by taking the differential pressure between the inlet and outlet of the circulator while pumping the system. This can be way more or way less than you compute.

Again, IMO.

Jamie Hall

the problem is...

if all four zones come off one header and return to one header -- that is, they are piped in parallel, as I would assume they are -- the flows in the various zones will adjust themselves so that the pressure loss -- the head -- in each zone is the same.  If all four zones were exactly the same, the flows would be too -- but that is unrealistic.  So the zone with the highest flow resistance -- probably the longest -- will have the least flow, and so on.  Then to add to the confusion, the total flow from the zones will go through the pump -- and the pump will operate at the point on its head vs. flow curve which matches the head vs. flow curve of the system (as usual).



But you don't add the head loss together.  You add the flows together at the same head.  There are formulae to do this, but they are messy and none too accurate.  Much better to take Icesailor's suggestion, and put in a flow meter and a couple of pressure gauges!

icesailor

Headache:

Jamie,

The thought of doing it the correct and "messy way", is already giving me a head ache just thinking about it.

furnacefigher15

Simple answer

Yes, the pump head requirement is calculated based on the loop with the highest friction to flow (usually the longest loop)



The flow in gpm the pump needs to move is calculated based on btu's the pump is responsible for moving at a desired temp rise.

Common design delta's are





20 degrees = 10,000 btu/hr per gpm (Standard)

25 degrees = 12,500 btu/hr per gpm

30 degrees = 15,000 btu/hr per gpm

35 degrees = 17,500 btu/hr per gpm

40 degrees = 20,000 btu/hr per gpm



Important note: You need to look at the actual pump curve of the pump to select the right one.



The generic descriptions that say

Example: Flow 0- 30 gpm Head 0- 15 feet



are misleading. Because what that means is that at 0 feet of head the pump will move 30 gpm. And at 15 feet the pump will move 0 gpm.

Gordy

Jamie is correcta

  My system is piped parallel actually its not that bad once you understand parallel piping. As Jamie explained head pressure equalizes itself, but flows do not. So balance valves, and piping the loops in equal lengths is important.



 Its also the head of the longest loop plus supply, and return piping, valves, fittings etc to, and from the boiler. Not the head of all loops combined. Flow rate where the pump curve intersects for the system would be divided equally amongst the loops in a perfect world as Jamie also explained.



 My system is ceiling, and floor radiant all piped parallel (23 loops) with a B&G HV circ running the whole show off one thermostat. If the radiant loops are sized according to the room by room heat loss it all works beautifully. So in my system the pump curve is 15 gpm at 11.5' of head. Divided amongst 23 loops would be .65 gpm each loop. Perfect world. I balance by return temps using the balance valves. So the flow is what it is.



So to answer the OP's question Longest loop not all loops combined.

But I'm a little perplexed as to why the need for zone valves if you are not zoning. All you did was spend money on unnecessary components, and creating more head loss in the system. Unless you plan on adding the t stats later.  Zone valves are for controlling different rooms, or loops with a t state to be able to run certain rooms at different temps. Some people like the bedroom cooler than the rest of the house etc.



Gordy

Ronbo

ty

I have an oversized boiler. A Weil Ultra 155 with a 129000 btuh output and only need 60,000 on design day so after trial and error with help from this site I have arrived at the conclusion to run all the zones together to keep my boiler modulating at 20% to 40% range at low temps (120 is the lowest i can go now) to make up for a poor choice of size in the boiler. Yes it was a waste of money for four zone valves in the end.

When all of my zones are slaved together to one thermostat the temps in all my zones are the same to within 1 degree of that thermostat so only one zone is needed for comfort anyway. With ODR I have a flat curve set from 115 low to 140 high. That keeps me stable with no cycling and longer burns (1hr to 2 depending on set back) but I would like to get the return temps a bit lower to widen the curve and also promote longer burns. I do have enough baseboard in all my zones ( 140 on design day is enough). Right now at 120 low my delta its only 4 degrees, if I go lower I will cycle. So I want more Delta if I can get it to promote a lower return temp. As I see it I can leave well enough alone or stack to get a bigger Delta. I am about to add 5000 btuh of radiant floor heat in zone 4 because it is the only room that needs help to even things up. I also want to add a garage space heater to use now and again as needed but not often.

So I now have three loops run in parallel running on three valves slaved together to open and close together.(they all run off a taco 008 now ,15 flow ,15 head) Zones 3 and 4 are only 4 feet above the pump ( upper floor) zone 1 is  4' below the pump. I know right now my flow is too great hurting my delta yes?

Zone 1 is 181 ft long (18,000 btuh of baseboard @ 140  degrees ( 10.84 head?) 1.8 gpm

Zone 3 is 161 ft long with 26,600 btuh of baseboard @ 140 degrees( 9.64 head?) 2.6 gpm

Zone 4 is  170 ft long with 14,000 btuh of baseboard @ 140 degrees(10.2 head?) 1.4 currently

Are my head calculations right?

Zone 2 was added to 1 because that’s where it belongs and it was only 14' of baseboard anyway. I want to use that spot for my garage heater or 5000 radiant floor loop combined. I am going to replace the taco 008 if needed depending on how things wind up.

If I add the radiant floor 5000 btuh to zone 4 it will become 19,000 btuh which evens things out in terms of flow. Basically 2 gpm needed for zones 1 and 4 and 2.5 needed for zone 3.

But the head on four would be raised to 17.4 because the radiant loop would be added (120 ft with transfer plates) this would widen the delta though on that loop which would help. Should the head balance matter? or is it the flow that I should balance?

Im thinking the Grundfos Alpha set to a constant pressure may work well for me yes? I would think if I can get all three zones to match closely in terms of flow I should remain balanced.

I could add the garage space heater to zone 2 location and use as needed then.