Circ.

kpc_40

a formula to figure out operating costs of a circ.?

Brad White_202

(A x V) / pf = Watts

Shorthand, Amps x Volts = Watts but there is a power factor, perhaps 92-95% which is divided into the A x V product, resulting in a larger number. The manufacturer may have that data; if not, 95% is reasonable.

Divide your Watts by 1,000 to get kiloWatts, the billable unit of measurement.

You can also take the nameplate Watts, but be warned that this number is a maximum draw. The actual Watts consumed will vary depending on flow and head, so take the clamp-on and multi-meter and have at it.

Once you have your measured Watts draw, expressed in kW, multiply that by the time of operation.

For example, say you have a circulator running at 115 Volts and drawing 0.6 Amps (69 Watts) with a 0.95 power factor gets you to 72.63 Watts or 0.07263 kW.

If the circulator runs 24 hours x 0.07263 kW that is 1.7432 kWH. If your rate is 18 cents, that cost would be 31.38 cents.

If you use the ECM type circulators, (Wilo or Grundfos), your savings will be much higher (and harder to predict) if these are set up using variable flow/constant delta-P or other modulating modes. Energy use goes down by the cube root in such cases, running an 80-Watt circulator down to less than 10 Watts.

kpc_40

I knew you...

you would have it. I looked at a botched job last week... the Grundfos 26-96 (2.3 amps)and a 007 is wired to run 24-7/ 365. that equates to nearly $100 per month. I am looking into a Ecm circ. I was unaware that Grundfos made one....

Brad White_202

Nothing wrong with

running the circulators you discovered as they have been running.. so long as there is a valid reason to do so! ...

As you well know, nailing down the required flow and head conditions means everything. Next is a means to throttle the emitters such as TRV's, to give a variable speed circulator (particularly an ECM), something to control to.

The Wilo Eco Stratos is currently available. The Grundfos Alpha and their newer Magna is going to be available in the US soon, but perhaps Canada has them for smuggling? I dunno.... January I was told but ask around.

Brad White_203

EDIT

I should have be more careful in that any circulator you install should have the appropriate UL/ETL listing should a mishap occur. My "smuggling" comment was half in jest, but it does bear risk which is not intended. I would wait until the circulators are available through regular channels.

Buzz G.

Circulators

Often I see the comment "constant circulation is the best" but in a converted gravity system using CI rads how can you say that is true? When the system pump is on the hot water is delivered, but when it is off (and the boiler is also off)the the radiators will cool down at essentially the same rate as with the constant circulation. This is because the rate of cooling depends on the radiation rates and will generate some gravity flow in the secondary circuit as most of cooling is going to happen in the rads.
This is why I am running my converted gravity system with a mod-con and a system circ that is controlled by the boiler's electronics (and the thermostat).

Brad White_203

Constant Flow

If you have a converted gravity system, consider this: Your system at it's inception did have constant flow. The comfort of a good gravity HW system is considered one ideal. That is the reason above all that the principle holds true by definition, gravity of all systems.

The principle holds true for pumped systems: The constant flow is married to nearly imperceptible changes in system water temperature. Radiators held to a constant and homogenous temperature emit heat at a predictable rate, ideally matched to your heat loss of course.

Now, if you have de-coupled your gravity system and are using an injection circulator (either modulating or on-off cycled), the effect on the secondary or radiation side will be similar, less perceptible changes in water temperature and hence room temperature.

If one cycles the hot water directly, the effect is mitigated by the higher mass cast iron sure, but you will still have peaks and valleys of temperature depending on the anticipation of your thermostat (or the differential setting on your controller to the same effect). A cycled system will demonstrate these peaks and valleys which one may or may not feel but which are measurable.

Cycled systems tend to be responding in a "catch-up" mode, depending on how far below setpoint the drop is before "on-time" commences. This may cause an artificial increase in temperature to reach setpoint on time. A constant circulation system can keep ahead of this, especially if the return water temperature is factored in as an indicator of heat transferred to the space.

(These peaks and valleys will be more rapid if you have copper-tube finned baseboard of course and such systems surely benefit more from constant circulation in the comfort department. So if constant circulation is to be favored, it would be these of all systems in my opinion.

With these older large-pipe gravity systems, the amount of pump head required is in practice so low that a good circulator, especially an ECM, will be enough to impart proper flow with minimal power. So you have the best of both worlds, high mass, lower temperature fluctuations and lower pump Watts to spend creating it. Such a deal.