Circulators or valves for zoning?

spyridon

Hi guys,
i'm renovating a house with radiant heating and a new wall mounted gas condensing boiler of 33kW (Viessmann, Bosch or Daikin).

House is a 233 square meter flat and want to have 3 zones. Each zone will have its own thermostat. Installation is dual pipe with central collectors and 14 radiators, total demand is about 24kW.

Zone 1 has 8 radiators (kitchen, living room/dinner table, guest room with guest bath)
Zone 2 has 3 radiators (master bedroom with dressing room and own bathroom)
Zone 3 has 3 radiators (daughter's room with own bathroom)

How do you recommend making the 3 zones, with zone valves using the boiler's circulator or with a hydraulic separator and 3 circulators, one for each zone?

Thanks,
Spyros

GEO80

Sometimes you may find when say one of 3 circulators is down, then you're glad to have two running. However a local on-site experienced/proven hydronic person would be great.

pecmsg

I prefer circulators. 

If one fails you still have heat b

HVACNUT

I didn't even know Daikin made mod cons. 
Whichever manufacturer, their I&O manual will guide you. Can all the names you listed spec that you can pipe 3 zones without P/S piping and using just the boiler circulator? I don't think thats a thing. Is it?

EBEBRATT-Ed

Zoning with circs is usually considered better. Having more circulators means you can still heat partially when one quits. Of course, you can usually open a defective zone valve too

ScottSecor

Unless we're working on a residential job with larger than typical zones, we're using zone valves. The average home around here requires about 50 to 70 thousand BTU output. With say three zones and 60,000 btu output, each zone requires say 2gpm. Why would I install three pumps for a total of 6gpm? Along with the pumps, I need more bx or mc, I need a few flow checks that always seem to start leaking over time, more flanges to crank/sweat/press and purchase, more bolts to crank, etc.

For most of these residential homes, one variable speed pump with a few zone valves seems to work best. If your really worried about pump failure, leave a spare in the box onsite. Takes about twelve minutes to swap the circulator if you use pump isolation valves.

Back to the OP, at 80,000 btu divided by three zones I suggest one variable speed pump with three zone valves. Not too many circulators readily available that are designed for 2.7gpm, but there are many that are designed for 8gpm.

Edit: I just re-read the original post and noticed you mentioned radiant heat. Then you went on to talk about a total of fourteen radiators. Should we assume you are referring to the radiators giving off "radiant" heat?

spyridon

Hi, total demand for water circulation is about 690 liters/h (3 gpm)

Zone 1 demand is 405l/h (1.77 gpm)
Zone 2 demand is 161l/h (0.72 gpm)
Zone 3 demand is 122l/h (0.54 gpm)

After mechanic's analysis, head for the most severe radiator is 0.3 meters (about 1 foot) (pipe distance is 95 meters back and forth, 14mm internal diameter PEX tube and asks for 58l/h - 0.26 gpm)

So if calculations are correct we need a circulator that can supply 690 l/h @ 0.3 meters (3 gpm @ 1 foot)

Can someone confirm calculations are correct?

PS. Yes, I was referring to the radiators

ScottSecor said:

Unless we're working on a residential job with larger than typical zones, we're using zone valves. The average home around here requires about 50 to 70 thousand BTU output. With say three zones and 60,000 btu output, each zone requires say 2gpm. Why would I install three pumps for a total of 6gpm? Along with the pumps, I need more bx or mc, I need a few flow checks that always seem to start leaking over time, more flanges to crank/sweat/press and purchase, more bolts to crank, etc.

For most of these residential homes, one variable speed pump with a few zone valves seems to work best. If your really worried about pump failure, leave a spare in the box onsite. Takes about twelve minutes to swap the circulator if you use pump isolation valves.

Back to the OP, at 80,000 btu divided by three zones I suggest one variable speed pump with three zone valves. Not too many circulators readily available that are designed for 2.7gpm, but there are many that are designed for 8gpm.

Edit: I just re-read the original post and noticed you mentioned radiant heat. Then you went on to talk about a total of fourteen radiators. Should we assume you are referring to the radiators giving off "radiant" heat?

spyridon

Even in a flat with some very low zone demands with only 3 radiators?

EBEBRATT-Ed said:

Zoning with circs is usually considered better. Having more circulators means you can still heat partially when one quits. Of course, you can usually open a defective zone valve too

spyridon

If supply from primary circulator is adequate for the system to follow no matter how many zones is there a point in making the whole system more complex? (hydraulic separator-circulators) Cost is no problem, just looking for the optimal solution

HVACNUT said:

I didn't even know Daikin made mod cons. 
Whichever manufacturer, their I&O manual will guide you. Can all the names you listed spec that you can pipe 3 zones without P/S piping and using just the boiler circulator? I don't think thats a thing. Is it?

spyridon

In this case you still have heat in the other zones but not in the one that the circulator is damaged. Would that not be the case with zone valves as well?
Of course if primary circulator fails in both systems you do not have heat at all.

pecmsg said:

I prefer circulators. 

If one fails you still have heat b

ScottSecor

For a run of 95 meters (312 feet) I come up with approximately 19 feet of head. That's a pretty long run.

My manual (rough) calculation is not always perfect, but here's the math:
312 feet x 1.5 = 468 468 x .04=18.72. I always round up, so call it 19 feet of head.

You appear to be outside the US, as you often refer to the metric system. I suspect when dealing with meters, kpa, ect. the pump head would not be in feet, but instead most likely in meters?

spyridon

@ScottSecor 314 feet / 0.55 in id pipe / 0.26 gpm gives a head of 0.5 feet (0.15m) according to an online friction loss calculator. See image attached. This is only for the pipe. Previous post had pipe plus fittings calculated.
The installation is with central collectors/manifolds and each radiator has its own dedicated flow and return lines.
Yes, I am giving metric but have also written imperial next.

ScottSecor

@spyridon I thing your gallons per minute calculations may be off.

For example to have a 20 degree Fahrenheit differential we use one gallon per minute for every ten thousand BTU. For example, if your system requires 80,000 BTU your pump would need to be able to circulate 8 gallons per minute (minimum). Assuming all three zones were calling on the coldest day of the year, this sounds about right. If you system can handle a wider temperature differential (say 30 or 40 degrees) the gpm requirements drop significantly.

It appears your from Austrailia, not knowing what area of the country I cannon guess your outdoor design temperature. Here in New Jersey, an average radiator is requires about 1gpm I guess on the coldest day of the year. Your house (flat?) appears to have 14 radiators. With my math that would require roughly 14 gpm to get that "standard' 20 degree delta T across the system. Even if you only need about a half gallon per radiator that still would require 7gpm total (or about 2.33 gallons per minute through each zone).

Finally as your chart explains, if you don't need to cram too many gallons through a pipe with internal diameter of .55 inches, the head pressure required is practically nothing. In my world, we

hot_rod

For those low flows one circ and zone valves. If a pump failure keeps you up at night, keep a spare on hand.

Zone valves can be manually opened if a motor fails, circulators, not so much.

spyridon

@ScottSecor Hi, I'm from Greece, typical med climate with usual max external temp -5C (23F)

I am calculating heating panels with 65/45C DT 20C and internal temp 22C, that is in imperial units 149/113F DT 68F

TOTAL FLOW in liters = totalKcal/DT Celcius

Yes, it seems head is extremely low.

Viessmann in their installation manual strongly suggest for flows below 400l and above 1400l to use a hydraulic separator. Why do you think that is? maybe because this is off the range of the circulator to work properly inverting the unit and regulating DT?

ScottSecor said:

@spyridon I thing your gallons per minute calculations may be off.

For example to have a 20 degree Fahrenheit differential we use one gallon per minute for every ten thousand BTU. For example, if your system requires 80,000 BTU your pump would need to be able to circulate 8 gallons per minute (minimum). Assuming all three zones were calling on the coldest day of the year, this sounds about right. If you system can handle a wider temperature differential (say 30 or 40 degrees) the gpm requirements drop significantly.

It appears your from Austrailia, not knowing what area of the country I cannon guess your outdoor design temperature. Here in New Jersey, an average radiator is requires about 1gpm I guess on the coldest day of the year. Your house (flat?) appears to have 14 radiators. With my math that would require roughly 14 gpm to get that "standard' 20 degree delta T across the system. Even if you only need about a half gallon per radiator that still would require 7gpm total (or about 2.33 gallons per minute through each zone).

Finally as your chart explains, if you don't need to cram too many gallons through a pipe with internal diameter of .55 inches, the head pressure required is practically nothing. In my world, we

spyridon

@hot_rod that was exactly my thought, why use 3 pumps to operate 3 zones that require very little flow? 2 out of 3 zones have only 3 heating panels.

The thing is that Viessmann in their installation manual strongly suggest for flows below 400l and above 1400l to use a hydraulic separator. Why do you think that is? maybe because this is off the range of the circulator to work properly inverting the unit and regulating DT? And this way the boiler works in constant effortless way and by regulating each zone separately you have a better hydraulic balance in the system?

in 2 out of 3 cases, if the zones operate individually the required flow is below 400l. Again that is only if they operate alone and not along with the other zones.

hot_rod said:

For those low flows one circ and zone valves. If a pump failure keeps you up at night, keep a spare on hand.

Zone valves can be manually opened if a motor fails, circulators, not so much.

psb75

A Viessmann boiler in the system is very good. Use their recommended hydraulic separator. Look at the manual for plumbing designs. Or use Caleffi's Idraulics manuals for design. Of course use ECM circulators. The debate about circulators vs. zone valves is...eternal.

hot_rod

The boiler has a minimum flow rate that it needs to operate properly. A small zone running may not provide enough boiler flow. So a separator or closely spaced trees will provide the separation. So you need a circulator for the boiler snd one for the zones. Idronics 15 is a good read
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf