I recently installed radiant in floor in a small zone in my home to compensate for a poorly insulated home and a heating system that was unable to keep up.
My radiant in floor system is tied to my hot water heater and uses a TACO 007 pump which is a pretty standard radiant in floor pump to deliver the water and in turn the BTU’s to my floor. I chose this pump because it is inexpensive and had a pump curve that was very close to what I needed.
No sooner had I installed the pump I asked myself, should I have done a DELTA T pump? TACO offers a pump called the BumbleBee which is a variable speed pump which modulates the flow based off of a fixed DELTA T which uses less power than the 007 I selected.
There are a few factors that make me choose what pump to use and they are cost of the pump, performance of the heating system and cost of operation. In this little write-up we are going to learn whether I made the right choice or the wrong choice in putting a fixed speed pump versus doing a variable speed DELTA T pump like the ‘Bumble Bee’.
In order to calculate my potential savings we are going to have to assume some numbers so lets start with some common variables.
On average in a cold climate a radiant pump runs for 12.5 hours out of the day during the winter. We then need to calculate the number of days in the winter that the pump will be running. We will go with 182.5 days which is a winter season of mid October to early April. The last number we need is my cost per KW which is 15.1cents per KW on average including delivery costs. ( Off topic: Doing a calculation of cost of operation and not including delivery charges on your power is going to give you a very skewed result )
NOTE: GAMA gas appliance manufacturers association indicates that in a cold climate a radiant infloor circulating pump will run for 2500 hours which is slightly higher than my calculated run times for the circulating pump.
Calculating the Cost of my 007 Fixed Speed Pump
The math to calculate how much a 007 TACO Pump costs to run is as follows;
- The Taco 007 Pump uses 81watts
- 81watts x 12 hours a day = .972 KW per day
- .972 KW x 182 days in the heating season = 176.904 KW per heating season
- 176.9 KW x 15.1 cents per KW = $26.71
My Total Cost to run an 007 Taco pump for a year is $26.71. My cost to purchase a Taco 007 pump is $90 on average.
Calculating my Cost of a Variable Speed Pump
Calculating the power consumption of a variable speed pump is pretty easy if you follow the proper guidelines which TACO is nice enough to supply. The Taco Bumble Bee variable speed ECM circulator runs between 0 and 42 watts, depending on the heating load. Let’s presume a wintertime average of 19 watts.
This average is based on the international standard that a circulator will run at full speed (design load) 6% of the time, at 75% of design load 15% of the time, 50% of design load 35% of the time, and 25% of design load 44% of the time. Based on this the HEC2 Bumblebee pump cost of operation works out as follows;
- The BumbleBee Pump uses 19watts on average all winter.
- 19 watts* x 12 hours a day = .228 KW per day
- .228 x 182 days in the heating season = 41.49 KW per year
- 41.49 KW x 15.1 cents per KW = $6.26
My Total Cost to run a TACO Bumble Bee Pump is $6.26 a year and my cost to buy the pump is on average $ 175.00
Summary of Potential Savings from a Variable Speed Pump;
My currently installed 007 pump was $90 and had I installed the bumblebee TACO Delta T pump I would have paid $175. Based off our rough calculations of cost of operation the bumblebee pump will save me $20.45 a year. This means the bumblebee pump would pay for itself in almost 4 years.
Worth it? Yes but not for the savings in electricity.
The Real Savings: Cant See The Forest for the Tree’s
People get fixated on the electrical savings of the TACO Bumblebee pump and they completely overlook the much larger item of fuel savings. My fixed speed 007 pump does not modulate to my heating demand which impacts not only the performance but the efficiency of the system.
If my heating system is designed for a 20 degree delta T and the flow increases it will reduce my delta T to as low as 10 degrees or worse which will bump up my return water temperature and impacts the efficiency of the boiler. This can result in $100 a year in extra fuel charges all because the wrong pump was used. As John Barba likes to say don’t step over a dollar to pick up a dime. The bumblebee pump is not just about electrical savings it is also about fuel savings.
In my radiant in floor system I currently have no actuators so my system curve does not change. My radiant in floor system is just on and off so my fixed speed pump is fine. My DELTA T is constant and so is my ‘duty point’ of the pump.
As I add the next phase of my radiant in floor and add actuators to give me control over heating to different rooms I will need to switch to a TACO delta T pump or I will not be delivering the right amount of BTU’s into each room which will impact efficiency and comfort.
In the end I should have put a bumblebee pump in instead of the TACO 007 pump primarily because as I expand my system my fixed speed 007 pump will definitely have an impact on my systems cost of operation and performance once I put a boiler into my house.