Robert O’Brien

ECM stands for Electronically  Commutated Motor, they’ve been around in the USA for close to 10 years but are really just starting to gain some serious traction. What are they? They are  pumps with permanent magnets that are electronically controlled  and usually variable speed, they  also convert the incoming AC current to DC.  Why is all that important? It uses  much less electrical energy and makes the pump speed completely variable.

Most existing small wet rotor circulator pumps are permanent split capacitor designs commonly called PSC motors and work just fine in most cases, with a couple of shortcomings, they use a fair amount of power,about 90 watts in most cases and are usually single speed or have three manually selected speeds that when selected converts the “3 speed” pump into a single speed  which may or most likely not be the right speed anyway.

Why switch to ECM pumps? What are the benefits to the contractor and the customer? Number one for both is the reduced electrical consumption with an ECM pump. Anywhere from 50-75 % reduction in power consumption. Pretty substantial savings on a percentage basis, but how much is that in dollars?  The run hours vary nationwide of course but are generally between 1800-3000 hours in the Continental USA.

Locally, in the New York area the number is 2000 hours and we pay about 23 cents Kwh or about $37 year to operate a PSC circulator. Half of that is an $18.50 savings per year, not a lot by itself but when considering the incremental cost to upgrade to an ECM, not a bad return on investment at all, about 45 times better than a money market account! It gets sweeter though, the 45 watts consumption of an ECM pump is at full speed and these are variable speed pumps.

How do they vary speeds? Some are Delta T pumps and vary speed based on supply and return temperatures to maintain a constant Delta T, usually 20 degrees in most systems. These pumps provide a benefit way beyond the electrical savings. How many systems run at the theoretical 20 degree Delta T?  Very, very few, usually due to over pumping, the circulator is just too big and the flow rate too high, which lowers Delta T and increases boiler cycling.  The reduction in boiler cycling will yield savings far beyond the electrical cost savings.

The other common style is Delta P pumps, these maintain a constant pressure by varying the speed. In response to increased or decreased resistance to flow. On a zone pump application, the Delta P pump will never change speeds, the system head never changes. However on a TRV or zone valve system resistance to flow will vary as valves open and shut and the pump will change speed to maintain a constant pressure. The variable nature of these pumps adds up to 25% to the electrical savings over a conventional PSC pump.

Should every new pump be an ECM pump? Probably most, but not all. It may not make economic sense in a zone pump system on rarely used zones, there aren’t enough run hours to justify the increased cost or in areas with very low cost electrical costs. The formula is,

(Run Hours) x (Watt Reduction) x (Cost per Watt) =  Annual Savings
Watts are Kw divided by 1000 !

What’s in it for the contractor to reduce consumers electrical consumption? Put yourself in the customers shoes, would you like to  do business with a contractor who is forward looking and concerned about the consumers best interest,striving to install and maintain the most modern, comfortable and efficient systems possible or a company that is happy with doing things the way they were always done with initial cost the only consideration?

Fuels costs vary widely but electrical costs are much more inelastic and are very slow to change making electrical bills stubbornly high while fossil fuel costs have come down from their highs quite a bit at least for now. Electrical costs will remain an issue of importance to consumers, why not be the guy who is offering the circulator equivalent of the LED bulb instead of the incandescent bulb guy?

Robert C. O’Brien is the owner of Technical Heating Co. LLC in Mt. Sinai, NY.

Zone valves and indirect water heaters? I’m guessing most guys would rather drink warm beer than install an indirect with a zone valve. Why? The answers given are usually the standard ones given about zone valves in general, slow recovery, not enough flow, bad practice, no DHW if circulator pump fails but in reality the real answer is the same as it most often is in this industry, “We always do it that way” I felt that way myself, but over the course of years I ran across many jobs with a zone valve on the indirect and, by and large, the customers weren’t complaining. I assumed they thought the reduced performance was normal so I asked them and they proceeded to tell me how long their teenage daughters were in the shower and how happy they were with their decision to buy an indirect. How can this be? After doing a little research, I decided to switch sides!

We install indirects with zone valves quite frequently and never have an issue. It’s a bit of a long explanation involving a fair bit of math but bear with me. Let’s assume we are installing a new boiler with  an indirect utilizing a zone valve. How do you size a pump for an indirect currently? To do it correctly you need to know the head loss of the piping, fittings and heat exchanger as well as the desired flow rate and then choose a pump that will meet the GPM requirements at the head loss of the system. How many people do that? Usually not too many! Most people will choose a 007 or to be on “safe side” a 3-speed pump so they can turn it up. If a pump manufacturer came out with a pump that had four speeds they could be like Spinal Tap!

For an example, lets use a popular 32-gallon indirect with a head loss of 1.9ft and a recommended flow rate of 8 GPM to achieve it’s rated first hour output of 165GPH at a temp rise of 77 F assuming a boiler temperature of 180F. What’s the head loss of the piping? The short formula which works pretty well is as follows.

    Total Linear Length x .06 = ft of head

There is approximately 4 feet of head per 100 feet of pipe run, 50% is added to account for fittings which gives us .06. But what about higher resistance devices installed in the piping, like flow valves and zone valves? These have to be accounted for separately and are rated by Cv. What the heck is Cv?

The Cv rating represents that amount of flow needed in order to create a pressure drop of 1PSI, or 2.31 feet of head, across a component like a valve. How do you convert Cv to feet of head? More math, unfortunately!

    (Flow in GPM divided by Cv)2 x 2.31 =  head loss

Lets use a zone valve with a Cv of 8 in our hypothetical installation, the higher the Cv number the less resistance to flow.

   (8 divided by 8) squared = 1 x 2.31  =  2.31 ft/head loss for zone valve

What about the piping? Lets assume we have 25 feet of piping from the boiler to indirect and back. Just a little more math.  25 times .06= 1.2 ft/head

Lets add it all up!

Indirect- 1.9ft

Piping- 1.2 ft

Zone valve 2.3 ft  for a total of  5.34 ft/head at 8 GPM. What size pump do we use? Taking a look at a pump curve chart  for a circulator that will provide 8 GPM at 5.5 ft/head, a 005  is pretty close but a 007 is a better choice.

What if we used a circulator and weighted flow valve on this job? Everything else would stay the same all we would have to do is swap out the head loss of the zone valve for the flow valve. What is the Cv of a weighted flow valve? A 1” NPT flow valve has a Cv of 6.7, the same valve in sweat is 7.7 Cv.  Remember, the higher the Cv the less resistance. The installation with a flow valve actually has a greater head loss than the zone valve job? Yes, it does!

This is how we can use zone valves on indirect water heaters with no homeowner complaints The caveat when using a zone valve on an indirect is domestic priority. Without priority you need to size the circulator for the zone with the largest head loss, which may not be the indirect zone and the flow rate for the all the zones combined.

Robert C. OBrien is the owner of Technical Heating Co. LLC in Mt. Sinai, NY. Robert serves as the Vice President of the national OESP chapter. See more from Robert in his blog “Boiler Sizing & Indirect Water Heaters” “Heat Loss Calculation on every residential boiler replacement?” & “Converting from Oil to Natural Gas.”

Zone valves and indirect water heaters? I’m guessing most guys would rather drink warm beer than install an indirect with a zone valve. Why? The answers given are usually the standard ones given about zone valves in general, slow recovery, not enough flow, bad practice, no DHW if circulator pump fails but in reality the real answer is the same as it most often is in this industry, “We always do it that way” I felt that way myself, but over the course of years I ran across many jobs with a zone valve on the indirect and, by and large, the customers weren’t complaining. I assumed they thought the reduced performance was normal so I asked them and they proceeded to tell me how long their teenage daughters were in the shower and how happy they were with their decision to buy an indirect. How can this be? After doing a little research, I decided to switch sides!

We install indirects with zone valves quite frequently and never have an issue. It’s a bit of a long explanation involving a fair bit of math but bear with me. Let’s assume we are installing a new boiler with  an indirect utilizing a zone valve. How do you size a pump for an indirect currently? To do it correctly you need to know the head loss of the piping, fittings and heat exchanger as well as the desired flow rate and then choose a pump that will meet the GPM requirements at the head loss of the system. How many people do that? Usually not too many! Most people will choose a 007 or to be on “safe side” a 3-speed pump so they can turn it up. If a pump manufacturer came out with a pump that had four speeds they could be like Spinal Tap!

For an example, lets use a popular 32-gallon indirect with a head loss of 1.9ft and a recommended flow rate of 8 GPM to achieve it’s rated first hour output of 165GPH at a temp rise of 77 F assuming a boiler temperature of 180F. What’s the head loss of the piping? The short formula which works pretty well is as follows.

    Total Linear Length x .06 = ft of head

There is approximately 4 feet of head per 100 feet of pipe run, 50% is added to account for fittings which gives us .06. But what about higher resistance devices installed in the piping, like flow valves and zone valves? These have to be accounted for separately and are rated by Cv. What the heck is Cv?

The Cv rating represents that amount of flow needed in order to create a pressure drop of 1PSI, or 2.31 feet of head, across a component like a valve. How do you convert Cv to feet of head? More math, unfortunately!

    (Flow in GPM divided by Cv)2 x 2.31 =  head loss

Lets use a zone valve with a Cv of 8 in our hypothetical installation, the higher the Cv number the less resistance to flow.

   (8 divided by 8) squared = 1 x 2.31  =  2.31 ft/head loss for zone valve

What about the piping? Lets assume we have 25 feet of piping from the boiler to indirect and back. Just a little more math.  25 times .06= 1.2 ft/head

Lets add it all up!

Indirect- 1.9ft

Piping- 1.2 ft

Zone valve 2.3 ft  for a total of  5.34 ft/head at 8 GPM. What size pump do we use? Taking a look at a pump curve chart  for a circulator that will provide 8 GPM at 5.5 ft/head, a 005  is pretty close but a 007 is a better choice.

What if we used a circulator and weighted flow valve on this job? Everything else would stay the same all we would have to do is swap out the head loss of the zone valve for the flow valve. What is the Cv of a weighted flow valve? A 1” NPT flow valve has a Cv of 6.7, the same valve in sweat is 7.7 Cv.  Remember, the higher the Cv the less resistance. The installation with a flow valve actually has a greater head loss than the zone valve job? Yes, it does!

This is how we can use zone valves on indirect water heaters with no homeowner complaints The caveat when using a zone valve on an indirect is domestic priority. Without priority you need to size the circulator for the zone with the largest head loss, which may not be the indirect zone and the flow rate for the all the zones combined.

Robert C. OBrien is the owner of Technical Heating Co. LLC in Mt. Sinai, NY. Robert serves as the Vice President of the national OESP chapter. See more from Robert in his blog “Boiler Sizing & Indirect Water Heaters” “Heat Loss Calculation on every residential boiler replacement?” & “Converting from Oil to Natural Gas.”