# delta p circulator or delta t?



## kuribo (Jan 5, 2016)

Hello and a Happy New Year to all!

I am finally getting into the final design and install of my gasifier boiler (Econoburn 200). Last summer I built a concrete block bunker to place the boiler, ran the lines 50' underground to my basement, spray foamed them, and have moved 2 500 gallon propane tanks into the basement. I have about 2400' of pex in floating slabs on the first floor (about 1000 sq feet) which I plan to split into two zones, and 4800' of pex in the basement (about 2400 sq ft), which I also plan to split into 2 zones.

I have been planning on feeding the 4 zone valves from storage with a motorized 3 way valve to set my supply temps with an outdoor reset control. I had been planning on using constant P circulators  (2 in case one goes out, I still can heat half the house). While looking at circulators, I was leaning towards the new Viridian delta P pump from Taco. Reading through their site though, they really push their Viridian delta T pump. I plan to use the Viridian delta T to charge storage in the "one and done" scheme, but can't really see where there is an advantage to using their delta T pump for a circulator over the delta P pump. Taco goes on and on about how the delta T pump is better for zone valved hydronics, but to me, it just looks like they use flow rather than temp, to meet the load. What am I missing? Any comments or advice as to which would be the preferred way to go?

Also, a quick question on storage inputs/outputs....I plan to use bushings into the propane tanks with elbows on the inlet and outlet dip tubes inside the tanks to direct flow horizontally. At what depth should I put the dip tubes? 

Thanks for any assistance....


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## Nofossil (Jan 6, 2016)

It's nice to have the choice, since there are cases where you really care about pressure, and cases where you really care about temperature. I haven't used their delta P model, but their delta T model actually has a couple of configurations - delta T and setpoint. I've used them in setpoint mode for boiler inlet protection, for instance. In that situation, I don't care what the flow rate (pressure, in this case) is, but I want a specific temperature.

I've also used them as injection pumps, where I inject hot water into a radiant loop to maintain a desired loop temperature. In the schematic below, P?, P2, and P7 are Viridian delta T models used in setpoint mode.


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## kuribo (Jan 6, 2016)

Thanks for your reply.

Yes, I plan to use the delta T Viridian for storage loading and maybe boiler protection- they definitely have their place. I am just wondering what the benefits of a delta T pump would be over a delta P pump as a zone circulator when using zone valves with in slab radiant....Taco seems to be saying it is better to control energy supplied by varying flow with the delta T pump, rather than temp. I don't see why...


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## Nofossil (Jan 6, 2016)

kuribo said:


> Thanks for your reply.
> 
> Yes, I plan to use the delta T Viridian for storage loading and maybe boiler protection- they definitely have their place. I am just wondering what the benefits of a delta T pump would be over a delta P pump as a zone circulator when using zone valves with in slab radiant....Taco seems to be saying it is better to control energy supplied by varying flow with the delta T pump, rather than temp. I don't see why...


Maybe the idea is to vary flow to get a desired return temp - not sure.


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## ewdudley (Jan 6, 2016)

kuribo said:


> Thanks for your reply.
> 
> Yes, I plan to use the delta T Viridian for storage loading and maybe boiler protection- they definitely have their place. I am just wondering what the benefits of a delta T pump would be over a delta P pump as a zone circulator when using zone valves with in slab radiant....Taco seems to be saying it is better to control energy supplied by varying flow with the delta T pump, rather than temp. I don't see why...



Taco would have you believe that the return temperature of a loop will vary according to the amount of heat required to maintain the temperature of the conditioned space.  This is of course nonsense.  The emitter can't see how fast heat is escaping from the space, all it knows is that it spends more time flowing and less time idle.

If multiple zones are being controlled with one deltaT pump, then yes, the pump will pump more flow when more zones are calling and will pump less flow when fewer zones are calling, but this functionality is better achieved with fewer failure modes by a deltaP or proportionalP pump available from more experienced deltaP pump manufacturers.


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## velvetfoot (Jan 6, 2016)

ewdudley said:


> a deltaP or proportionalP pump


Are they the same thing?  I am curious, I have several B&G ecocirc Varios, and B&G notes that the Auto version is proportional pressure.


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## kuribo (Jan 6, 2016)

ewdudley said:


> If multiple zones are being controlled with one deltaT pump, then yes, the pump will pump more flow when more zones are calling and will pump less flow when fewer zones are calling, but this functionality is better achieved with fewer failure modes by a deltaP or proportionalP pump available from more experienced deltaP pump manufacturers.



It seems like they want to vary flow, rather than temp, to control heat output. With a delta p pump, zone valves, and a mixing valve controlled by outdoor reset, you would keep flow constant and vary supply temp. Seems like you would have a much greater range of control with the varying supply temp.

Who would you recommend as a more experienced delta P pump manufacturer?


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## maple1 (Jan 6, 2016)

I'm only using mine in a simple setup, 5 zones with 5 zone valves and one pump - but I absolutely love my Grundfos Alpha.


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## ewdudley (Jan 7, 2016)

kuribo said:


> Who would you recommend as a more experienced delta P pump manufacturer?


I was just getting cute with Taco for taking so many years to finally offer pressure controlled ECM cirulators.

I don't have any industry experience or any knowledge of bona fide comparative reliability analyses that would qualify me to recommend any particular brand or model.

Just judging from the positive experiences of we system designers and operators here in the boiler room, it would be rather hard to go wrong with any of the pressure controlled ECM pumps, Taco models included, so long as the size, pump curve steepness, and feature set meets the requirements of the application.


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## ewdudley (Jan 7, 2016)

velvetfoot said:


> Are they the same thing? I am curious, I have several B&G ecocirc Varios, and B&G notes that the Auto version is proportional pressure.



Here's a good presentation on the difference between deltaP an proportionalP:

http://spacepak.com/hydronictraining/HydronicTraining.pdf

"Proportional differential pressure control is best for systems where the heat source and/or "mains” piping leading to the load circuits dissipate a substantial portion of the circulator head."  The classic example is a bunch of radiators, each with its own TRV, with long supply and return manifolds.  When the TRVs flow more it takes more pressure to overcome the friction losses of the manifolds.

In a typical multi-zone system with zone valves connected to short fat supply and return manifolds near the heat source, deltaP makes more sense.


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## JP11 (Jan 7, 2016)

Are you trying to use a delta T circulator as your ONLY boiler protection?

I'm not positive about set point mode... but I think that would be a very bad idea.  In delta T mode, the pumps run full power for 2 minutes before starting to adjust.  I don't think it's a very good idea to think this technology will protect you from a big slug of cold water going into your boiler jacket and shocking it.  A thermal device like a Danfoss is more appropriate IMHO.

Love my delta T circs.  the other day when 5 zones in the house were calling.. and 4 pumps were running.. I added up the current and it was 1/3 of the previous amount when using 00R circs.

JP


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## Nofossil (Jan 7, 2016)

JP11 said:


> Are you trying to use a delta T circulator as your ONLY boiler protection?
> 
> I'm not positive about set point mode... but I think that would be a very bad idea.  In delta T mode, the pumps run full power for 2 minutes before starting to adjust.  I don't think it's a very good idea to think this technology will protect you from a big slug of cold water going into your boiler jacket and shocking it.  A thermal device like a Danfoss is more appropriate IMHO.
> 
> ...


For the drawing I posted (and for my own system), the bypass circ is the only boiler protection. When it starts (at full speed), it's just circulating the water that's in the boiler through the boiler. Other than a bit if water in the near-boiler plumbing, there's no additional cold water introduced. If the boiler isn't stone cold, the water at the top is warmer than the water at the bottom, so circulating it is a good thing - reduces the time that and boiler metal is below condensation temp.

A Danfos would also prevent me from preheating the boiler from storage.

Might not be the case in all configurations, though.


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## velvetfoot (Jan 7, 2016)

Nofossil said:


> A Danfos would also prevent me from preheating the boiler from storage.



I'll have to look at your bypass setup again.


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## Nofossil (Jan 7, 2016)

velvetfoot said:


> I'll have to look at your bypass setup again.


Look at the live link in my sig to see my setup.

If / when I break open the plumbing toolbox again, I'll move the boiler circ above the boiler and above the recirc loop tee. That way I won't have to run my boiler circ at all during warmup.


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## Nofossil (Jan 7, 2016)

I'm a big fan of maximizing and maintaining stratification, which means minimizing turbulence. I like to see horizontal flow as close to the top and bottom as practical. Larger diameter reduces velocity as well.

However, I don't have any actual data about how important that is.


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## kuribo (Jan 7, 2016)

As close as possible meaning the top dip tube is say 0.5" from the top of the tank, the bottom tube, 0.5" off the bottom, or????

As I said in the original post, I will have elbows to direct the flow longitudinally/horizontally along the propane tank long dimension....just need to know where people are putting them in relation to the top and bottom of the tank...

Thanks.


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## Nofossil (Jan 7, 2016)

Any water above the top port or below the bottom port will pretty much just stay there, so as close to the top and bottom as practical seems right to me.

I have a client with *very* expensive commercially produced heat storage tanks where the inlet and outlet ports are more than 12" from the top and bottom of the tank. It dramatically reduces the useful capacity as you'd expect.


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## kuribo (Jan 7, 2016)

Yeah, I figured that....Just didn't want to get too close to the top or bottom due to boundary effects...


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## Bob Rohr (Jan 9, 2016)

Ideally you want to pipe into and out of the tank from the side.  That will reduce the amount of mixing in the tank.  You can buy or build a sparge tube if you need to go into the top of a tank.  It basically spreads the flow evenly across the top or bottom to prevent breaking up the thermocline.

Here is some good reading about tank design. piping and calculations.

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

Be careful with ∆T pumps for boiler protection, it is best to use two pumps to provide absolute protection, especially with big cold loads possible.  I don't agree with the drawing shown in the Taco installation manual.  A large cold load, like a concrete slab, large buffer tank, or a building with cast iron rads,  would be no match for that piping method.

The drawing below works with a delta t and fixed speed circ.

A 3 way thermostatic valve is simpler yet for boiler protection and only requires one pump.

If you plan on using zone valves or TRVs a ∆P circ is the better choice. 

 That concept that a distribution circuit wants, or needs to stay at a pre-determined ∆T to be most efficient is a bit of a stretch.

When a system starts from a cold start you have and want a large ∆T.  You move the most energy with large deltas.  As the system warms the delta decreases.  Attempting to "fix" a delta may result in low flow rates, and a lack of heat transfer as the flow goes laminar.

Also the delta T you design for in the distribution side depends on the type of heat emitters.  Radiant floors like a 10- 15 delta to keep an even temperature across the loop length.

Panel rads work fine with 30 or 40 ∆T as the surface temperature is not as critical if you are not standing on them


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## velvetfoot (Jan 9, 2016)

On the tank, for me, with a pellet boiler and buffer tank, the tank is to absorb excess heat that the load cannot.  Even though there is some stratification when loading, and my tank has internal baffles (they say), I don't care if it's stratified when the boiler is on because the way it is piped up, it is supplying the load.  When the buffer tank gets full and the boiler shuts off, that is when stratification comes into play.  The zone circulators draw off the top of the tank and return to the bottom, and the tank cools down from the bottom up, as it should.

I guess with a large storage tank there are other issues that might come into play, but if a session of wood loading loads up the storage tank, I'd think it'd be similar.  It's more important on the drawdown.


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## BoilerMan (Jan 9, 2016)

As has been said in this thread in various ways, we all agree that there is no better boiler protection than primary/secondary piping in one configuration or another.  Even an ESBE thermic valve is a type of pri/sec piping arrangement if you will, as it decouples the boiler from the load with large loads such as storage. 

I find that the added mixing with a boiler primary pump really helps get the heat plant above condensation temps as quickly as possible at a cold startup.  Also if you have any other type of boiler (oil, gas, electric) in the mix as a backup, I would recommend piping it in such a way as to have the ability to pre-heat the wood boiler to avoid lots of condensation from a long period of no fires.  I burn a bit of oil to heat mine up if its below 75F after mixing with boiler primary pump. 

TS


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## huffdawg (Jan 10, 2016)

maple1 said:


> I'm only using mine in a simple setup, 5 zones with 5 zone valves and one pump - but I absolutely love my Grundfos Alpha.


I had a grundfoss alpha it died after roughly two years...   I think they dont like power outages.


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## velvetfoot (Jan 11, 2016)

Nofossil said:


> Look at the live link in my sig to see my setup.


May I ask the purpose and rules for the zone tank valve?  I'm attracted to the concept of controlling boiler flow to my storage (buffer) tank, and locking it out when the boiler is on, since I can modulate the boiler down to match zone load.


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## Nofossil (Jan 11, 2016)

The tank zone valve is for charging the tank - when open, it allows top-to-bottom flow through the HX coil, using the wood boiler circulator. In that mode, storage is just another zone that I can put heat into.

The storage circulator is for heating other zones from storage. In that mode, flow is bottom-to-top through the HX coil.


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## Nofossil (Jan 11, 2016)

For NFCS and Vesta folks, these are the rules that govern the tank zone valve:

Set *Tank Zone Valve* to *TRUE* if *~Storage Capable* is true and *~Really Cold* is not true and *~Wood Boiler Active* is true
Set *Tank Zone Valve* to *TRUE* if *~Wood Boiler Overheated* is true
Set *Tank Zone Valve* to *TRUE* if *~Storage Capable* is true and *~Virtual Demand* is not true and *Wood Mode* is true
Set *Tank Zone Valve* to *TRUE* if *~Storage Capable* is true and *~Wood Boiler Hot* is true
Set *Tank Zone Valve* to *TRUE* if *Preheat Timer* is true


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## velvetfoot (Jan 11, 2016)

Nofossil said:


> The tank zone valve is for charging the tank - when open, it allows top-to-bottom flow through the HX coil, using the wood boiler circulator. In that mode, storage is just another zone that I can put heat into.


I like that a lot for my pellet boiler.  "If boiler temp = (say) 178, valve opens to charge tank, boiler temp = 175, valve closes".  No excess hot water going to storage, boiler modulates, temperature flow to load high. Heat only going to storage when there actually is excess while modulating at 30%.  A mixing valve, mixing water going to the tank with the bottom of the tank, set to 178 or whatever, might make things smoother, bring less cooler water from the bottom of the tank back to the boiler, and keep the boiler from changing it modulation drastically.  1.25" mixing valves are expensive though, I imagine, as I imagine 1.25" zone valves.

I like the concept a lot though.  Why send heat to a buffer tank if it's not necessary?

Edit: Thanks for the rules.  It helps this non Vesta person as well.

Edit:  DHW comes from a pipe inside the buffer tank, so it can't get too cool.


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## Nofossil (Jan 11, 2016)

velvetfoot said:


> 1.25" mixing valves are expensive though, I imagine, as I imagine 1.25" zone valves.


I just used a 3/4" zone valve. They make models with a fairly high CV, and you don't need much flow if you can achieve high delta T from good tank stratification.


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## velvetfoot (Jan 11, 2016)

Nofossil said:


> I just used a 3/4" zone valve. They make models with a fairly high CV, and you don't need much flow if you can achieve high delta T from good tank stratification.


Alas, I must make do with what I have, which is a 1.25" pipe that goes in the top that has bi-directional flow.


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