Variable Circulator controlled by d/p?

imatellerslie

I am planning to use a home run system using pex to supply 20 radiators. I am going to put a TRV on each radiator, and plan a constant circ system. I had considered using a large circulator that would provide the necessary flow to all the radiators with all TRV's full open, and a pressure relief between the supply and return manifolds to maintain the pressure differential, but this seems pretty wasteful of electricity to me.

I was wondering if anyone has used a variable speed circulator controlled from a pressure sensor to keep a constant d/p between supply and return headers. This way, the pump would only use enough electricity to supply current flow requirements.

What if all the TRV's go shut? If the d/p sensor is trying to maintain 15psi, then the pump would just cycle, right? I don't know how to design it to overcome this problem.

Thanks in advance for your help.

Doug_7

Differential pressure control

Pump speed controlled by differential pressure is the smart way to minimize pump power use. The typical differential pressure bypass wastes all of the pump power required to produce the bypass flow.

Pump speed controlled by differential pressure is commonly used for domestic water booster pumps to supply adequate domestic water pressure to the upper floors of high rise buildings.

If all the TRV's go shut the pump will not cycle - the pump speed will just back down to a lower speed sufficient to maintain the differential pressure setpoint at zero flow. This may be about 30 or 40% of full pump speed. These pumps are not positive displacement - it takes some pump speed to generate the differential pressure even at zero flow.

In Europe Grundfos makes a Magna pump that does this automatically - pump speed controlled by internal differential pressure. Not yet available in North America. They claim up to 70% savings in pump power. Not unreasonable considering that when you cut pump speed by 20% the pump power is reduced by almost 50%

You can control pump speed by differential pressure in a two-pipe system (supply and return) and you do not need or want a differential pressure bypass valve at the end of the supply and return headers. I do provide a very small 1/4 inch tubing bypass at the end of the supply and return headers to avoid zero flow.

This would not work on a one-pipe system where a high circulation flow is required to induce a flow through the radiator.

imatellerslie

Thanks for the reply Doug. I wish I could get ahold of that Grundfos pump with the internal d/p control.

Wouldn't one of these centrifugal circulators cavitate, even if its speed is reduced to 20% of max RPM, if there is zero flow? I hadn't considered the 1/4" bypass line that you mentioned, but I might. I had considered piping copper for the supply and return headers, using a reverse return to try to keep d/p the same for all the radiators, but decided that I'd like a home run system with Pex-al-pex better, particularly with the current price of copper.

Anybody else have any experience with using d/p to control a circulator's speed?

Doug_7

Pump will not cavitate at zero flow

The circulator will not cavitate at zero flow. I know this because I am doing it with a Grundfos UP 26-99 pump operating at full speed. The only possible cause for cavitation would be serious overheating, which does not occur because there is enough heat loss from the pump and piping to prevent any noticable heating. The main reason for the 1/4 inch tubing bypass line is to guarantee there will always be a very small flow adequate for cooling.

Anybody else have any experience with using d/p to control a circulator's speed?

imatellerslie

Thanks again Doug...

hearing from someone with experience doing this is very valuable to me. Are you using an external pressure sensor to send a control signal to the Grundfos?

Oh...I see you said its operating at full speed...

Are there any variable speed pumps available in the US market?

tim smith

delta P & variable speed

B&G makes a variable speed pump, think it's their VS series. And then you could use a Heattimer Delta P controller to do what you want. Good luck.

imatellerslie

Thanks Tim...

I'll check that out.

Mike T., Swampeast MO

Can't seem to find the Heat-Timer delta-p controller you're referring to. Closest thing I saw is below--but it's a single pressure sensor not a differential.

http://www.heat-timer.com/?page=coc

No search feature that I could find at Heat-Timer. Could you possibly post a link?

Aidan (UK)

Yes, but...

"Anybody else have any experience with using d/p to control a circulator's speed?"

Yes, but only with commercial pumps, using static or differential pressure sensors. In all cases, the pressure sensor output was 4-20 mA. This was input to a BMS/DDC outstation, which calculated the appropriate pump speed (0 to 100%) and supplied a 0 -10 V control signal to an variable frequency inverter drive. This is expensive technology and it's not practical for domestic applications. I think you'll have to wait for Grundfos to launch the Alpha or Magna pumps in the US. If they get enough enquiries, they may realise there is a demand.

Some inverters have built in pre-programmed control software, so that they just have to be connected to an appropriate sensor input (usually 4-20 mA) to provide a controlled PID output speed. Inverters don't work with single phase motors, but you can get single phase input/3 phase output inverters.

If you have constant flow on the radiator circuit, you'd probably have a variable temperature system,i.e., outdoor reset or similar. The flow temperature would then reduce under partial load conditions, so it's less likely that all the TRV's would be shutting the flow right down; it's less likely that you would get noise from the TRV's at low flow rates, this being a regular problem.

imatellerslie

I do plan to use outdoor reset to

...control the temperature in a buffer tank, with a geothermal unit as the heat source. I hadn't really thought about the fact that the TRV's wouldn't have to throttle much with the fluid temperature going down as outdoor temp goes up; that's a very good point.

Incidentally, I noticed that the B&G and Grundfos variable speed circs both use 0-20 mA/4 to 20 mA or 0-10V/2-10V input signals. So I believe I can use the output from a pressure sensor directly connected to the pump.

I wonder if I'll save more energy by using outdoor reset with relatively constant flow, or by using a variable circ with a constant setpoint aquastat on the buffer tank. In one case, I save energy by raising the COP of the geothermal unit, and in the other case, I save energy at the circulator. I'm thinking I'll probably save more energy by letting the compressor in the geothermal unit spin under less load and raise the COP.

Aidan (UK)

Variable speed pumps

I think I'd use the outdoor reset to control the flow temperature of the radiator circuit, with either a 3-port mixing valve or an injection pump regulating the heat flow from the buffer tank. I'd be concerned that the heat pump would be doing frequent starts if it's stopping temperature were turned down under part-load conditions. It could overheat and burn out a motor. With water chillers, the manufacturers usually recommend the system should have a minimum water volume for this very reason; the volume of water allows the compressor motor to run for some time when there is little cooling demand. I don't know much about heat pumps, so don't know which strategy would be best.


I thought the Alpha pump sold here has an integral dP sensor. I've never used one of these pumps with a built-in inverter, so don't know the technical details. The dP sensors are expensive.

imatellerslie

I think with an adequately sized buffer tank...

the geothermal unit won't cycle excessively. That, and my desire to decouple the radiator flow hydraulically from the geothermal unit flow, is my reason for using a buffer tank.

I definitely don't want to burn up the compressor. Lowering the operating temperature of the system will significantly increase the efficiency of the geothermal unit, since it will be much easier to "pump heat" from the ground loop to the system if the system temperature is lower. I'm not too familiar with the aquastats, but I think as long as I can set it with a reasonably large differential, and have an appropriately sized buffer tank, I should be able to minimize compressor cycling, particularly if the secondary is set up with TRV's and constant circ. It will be a HUGE heat sink for that geothermal unit.

I wish the pump with the integral d/p sensors were available here. Maybe I should take a European Vacation to get one. :-) (Unlikely with all the money I have to spend on my house)

[Deleted User]

Heat Timer makes

a Model MC Series Analog Control 4-20mA or 0-10VDC that will work w/ the B&G VS Pump.

The Model Number for the 0-30 PSIG Control is MCA-30P. The Catalog Number is 929502-00.

The VS Pump can turn down from 3500 to 750 RPM. The capacities are pretty robust & may not lend themselves to a residential application. You can probably view the curves @ www.bellgossett.com. A word of caution. These pumps use permanently lubricated ball bearings. Can be noisy.

imatellerslie

Thanks Ron...

I'll check out those leads. I've been to both sites, and looked at the B&G VS circ, but I couldn't figure out which Heat Timer sensor to use.

Kenny

check thisout

http://www.magna.grundfos.com/

imatellerslie

I sure hope

...I can get one of these. That's an amazing product, and fun too!

Rich Corcoran_12

Differential pressure

is the typical way a vs pump is controlled in a european heating system. Grundfos makes several pumps with on-board vs drives and controls. These pumps are unavailable in the North American market at this time, principally due to the significant hurdle (cost)of meeting North American requirements (UL, 60hz.......).

We do have a line of integrate VS pumps available in the US. You would need to provide a 0-10vdc or 4-20ma signal from a dp control.

Feel free to contact me directly with any questions.

Mark Eatherton1

Hiya Rich!!

Long time no see...

ME

imatellerslie

Thanks Rich...

I'll be in touch.

Constantin

Expensive technology?

I think not. Otherwise, you wouldn't see it in compressors, washing machines, etc. A simple brushless DC motor with a PWM driver should do the trick nicely. This technology is getting less expensive every year as manufacturers of motors stop being able to value-price their wares.

Aidan (UK)

Expensive technology

To the best of my knowledge, there are no pumps with brushless DC motors and PWM drivers marketed (possibly the Grudfos Magna is such a beast, but I don't know).

To custom build such a set-up would require some technical knowledge, which is not cheap. It may be the cheapest option for OEMs but is not yet available to the average home-owner to control their pumps. It is getting less expensive, but it's not generally available yet. All the variable-speed pumps and fans I dealt with were monitored and controlled via BMS outstations which were expensive.

jerry scharf

Expensive, I think so!

OK,

I was trying not to post on this link, but this one I couldn't let go. Wilo produces a ECM motor VS pump, stratos, with built in dP controls (or dT or external input.) I have talked to them, and the current state of the product is: no UL approval, metric pipe thread mounts only, 230VAC. I checked, and they will work fine on 50 and 60 Hz power (it's rectified to DC anyway.) They tested it in their lab to be sure.

They have wonderful energy efficiency, but they are quite "dear". I won't talk price, but say it is probably more than 4x the cost of a comparable curve fixed speed wet rotor pump.

I'm still considering it for my house, but that's a big chunk of money to tie up in one part.

jerry

Mark Chaffee

All you need is a Taco Variable Speed “00” Circulator

All you need is a Taco Variable Speed “00” Circulator.

What you are trying to do can be accomplished in a number of ways, but the way we see it done most frequently is on commercial Taco LoadMatch systems, where the variable speed pump feeds a terminal unit. The differential pressure sensors gives the pump a 0-10V(dc), 0-20 mA, 2-10 V(dc), or 4-20 mA signal. The pump is available in any version 003-0014. All you add to the front is 00-VV (Variable Voltage), so a 007-F5 would become a 007-VVF5.

Another way to accomplish what you are doing is by differential temperature instead of pressure, as the pressure transducers are still viewed as being expensive for normal residential applications. You can do 5-50 degree delta T with all connections (line and low voltage) being made directly to any model Taco “00” Circulator. That pump would be a 00-VS (Setpoint).

The Setpoint pump can be configured to do differential temp, dial-in a specific set temp (30-210 degrees F), be direct or reverse acting, linear or logarithmic output, provide boiler protection or boiler protection as a limit control (75-165 degrees F).

I have attached the pdf of the catalog sheet for you reference.

P.S. Also check out the “00” circs with the built in outdoor reset.

P.S.S. If you prefer using valves, we also have outdoor reset and setpoint versions available in the iSeries Mixing Valve. Pdf attached.

Mark Chaffee

All you need is a Taco Variable Speed “00” Circulator

All you need is a Taco Variable Speed “00” Circulator.

What you are trying to do can be accomplished in a number of ways, but the way we see it done most frequently is on commercial Taco LoadMatch systems, where the variable speed pump feeds a terminal unit. The differential pressure sensors gives the pump a 0-10V(dc), 0-20 mA, 2-10 V(dc), or 4-20 mA signal. The pump is available in any version 003-0014. All you add to the front is 00-VV (Variable Voltage), so a 007-F5 would become a 007-VVF5.

Another way to accomplish what you are doing is by differential temperature instead of pressure, as the pressure transducers are still viewed as being expensive for normal residential applications. You can do 5-50 degree delta T with all connections (line and low voltage) being made directly to any model Taco “00” Circulator. That pump would be a 00-VS (Setpoint).

The Setpoint pump can be configured to do differential temp, dial-in a specific set temp (30-210 degrees F), be direct or reverse acting, linear or logarithmic output, provide boiler protection or boiler protection as a limit control (75-165 degrees F).

I have attached the pdf of the catalog sheet for you reference.

P.S. Also check out the “00” circs with the built in outdoor reset.

P.S.S. If you prefer using valves, we also have outdoor reset and setpoint versions available in the iSeries Mixing Valve. Pdf attached.

imatellerslie

Thanks Mark...

this is very helpful information.

Mark Eatherton1

Hey Mark...

Tell Dave to send my commission check soon:-)

ME

Kal Row

posted part of this in another thread

please see and comment
http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=14946&mc=30#Message90281