White Paper: D’MAND CIRC
Guide to the D’mand Circ Text:
Reducing High Energy Bills Related To Central Water Heating Systems – A Guide to D’MAND CIRC® Applications
Identifying Good Building Applications, Estimating Savings, Supporting Data
The D’MAND CIRC is a recirculation pump used for domestic hot water that operates based on user demand within the building as well as temperature of the recirculation loop. It will run intermittently, as needed, throughout the day running an average of 1 hour vs. the 24/7 continuous pumps that are currently in use.
By operating in this fashion, the recirculation loop temperature is allowed to cool during periods of non-use, slowing down heat losses, and kick-starts the temperature back to normal when someone does need hot water. The pump electricity is reduced by over 80%, but more importantly, the heat radiating from the recirculation loop is reduced by over 50%, which can result in an overall 10 to 30% reduction in the water heating energy consumption.
Refer to the following sections to learn about the best applications of the D’MAND CIRC and simple ways to estimate savings.
Best Building Types:
Here are some general indications of the type of buildings that work well. It is split into 3 tiers, but there is no fine line between the tiers as specific characteristics of a certain building type can influence the savings.
Tier 1 – Highest Impact:
Multifamily (20+ units), Hotels, Motels, Condos, Dorms, Barracks, Hospitals, Some industrial
Tier 2 – Mid Impact:
Multifamily (under 20 units), Gyms, K-12, Airports, Arenas, large offices
Tier 3 – Lower Impact:
Small Healthcare, small office, retail store, supermarket, restaurants, warehouse
Characteristics of Ideal Applications:
Since this is a technology that primarily slows down heat losses from the recirc piping. The more piping there is, the greater the distance that the pipe travels throughout the building, the larger the difference between the temperature of the pipe (which is close to the temperature setpoint of the system 120 to 140 degrees F) and the surrounding environment (ambient air temp, cold ground temp if in ground, etc…), the higher the savings. Look for these attributes to find the slam dunk applications:
- Higher Domestic Hot Water Use
- Large Structures with water use spread out
- Inefficient Water Heaters (Sediment, low EF rating, etc..)
- High Water Heater Temperatures Needed or Wanted
- Pipe running in unconditioned spaces (crawl spaces, garages, outdoors), underground or under slab
- Many Gallons of Hot Water Storage (200+)
- Exposed Piping that you can place the temp sensor at the last unit on the loop*
*If the loop is exposed (such as in a subterranean garage), sometimes you can identify the last point at which hot water is needed and wire the temperature sensor which shuts off the unit at this point. In a scenario like this, you can cut off hundreds of feet of heated pipe that is unnecessarily hot.
Characteristics of Energy Wasteful Recirc Loops:
- Not Insulated
- Running 24/7
- Oversized Pump
- Long return lines or a far distance between the boiler room and the last fixture that uses hot water on the loop
- Running through unconditioned space or other materials that act as heat sinks such as underground, clamped to concrete, etc…
- Long branches off the main loop before it gets to the fixtures*
- Broken Pumps*
- Closed/Broken Valves*
*starred items are water wasteful and may or may not be energy wasteful
Simple Ways To Estimate Savings:
As the manufacturer of the D’MAND CIRC system, our official savings claims are a reduction in your water heating energy between 10% and 30% and pump electricity reduction of more than 80%. These claims are dependent on the specific characteristics of the application.
From all the various case studies conducted (next section), the most obvious trend has been that a small building will have a high proportional saving (20 to 30% off the water heater energy) while having a relatively smaller absolute energy saving value (400 to 1000 therms), while bigger buildings have a lower proportional savings (10 to 20%) while have a larger absolute energy saving value (1000+ therms).
This makes sense as the larger buildings will have more frequent occurrences of demand, therefore less down time between uses to save energy. Whereas the smaller buildings have less frequent hot water events and therefore longer periods of time to save energy.
While it can be very tough to accurately model heat losses from the loop (too many variables and most are unknown), some general trends have appeared.
The following are some rules of thumb that we use:
- 30 therms saved per unit per year
Or use the following table to determine narrow in on estimating the savings off a percent reduction from the bill.
|15%||500 to 999|
|20%||300 to 499|
These will be updated as more data is received.
It should be noted that estimating the pump electricity savings are much easier and more accurate, but you need to know the information on the pump you are replacing.
If it’s a small pump, 85 watts, then the savings will be around 700 kWh, if it’s a bigger pump (200 watts), then the savings will be around 1600 kWh. We have even replaced 500 to 800 watt pumps. Just assume that with D’MAND CIRC the pump will run 1 hour a day, compared to running 24/7 on the pump that is being replaced. You can use the nameplate information to figure out the rest with some simple calculations.
Circulator pumps are used to reduce the wait time while waiting for hot water. Hot water is available quickly, but with the tradeoff of tremendous energy waste. This is the dilemma between water efficiency and energy efficiency. Using the D’MAND CIRC is the best of both worlds; you get hot water quickly, but without the energy waste. Even though the D’MAND CIRC only runs on demand and when there isn’t a suitable temperature (above 100°F), does not mean there is the tradeoff for waiting for hot water. Here’s why:
- It only takes 1 use, anywhere in the building, to prime the entire loop
- A primed supply line takes up to 3 hours to fall below a suitable hot water temperature
- By Default, the D’MAND CIRC auto-primes the loop every 5 hours
- It takes roughly 50 seconds to purge 250ft of 1-1/2” supply line, which is only possible (to wait an extra 50 seconds) if you are the very last tenant on the supply line AND it’s been about 3 hours since the last hot water use by anyone in the building, but not more than 5 hours since the auto-prime feature will have kicked in. The probability of this chain of events approaches zero.
- D’MAND CIRC is currently in over 1,000 buildings, from luxury resorts, to large apartment buildings with as many as 189 units on one recirculation loop without any unsolvable issues.
D’MAND CIRC saves water by fulfilling its function as a recirc pump, and test data has in fact shown more water savings than a continuous pump. Preliminary studies thus far, in 26 buildings have resulted in an average of 2% reduction in the buildings entire water use (Please note that this data is highly variable). In the Marriott Case study, where water meter reads were taken over 52 weeks, making it the largest data set in this area, showed a 4% reduction in water use for the year.
History of Case Studies:
Here are brief summaries from case studies conducted on D’MAND CIRC. This is supporting data that helped guide us towards the savings estimations. In total data came from about 50 buildings, which is not a big enough sample size to be statistically sound, but more indicative of what we would expect. Hundreds of thousands of dollars were spent on these studies with millions of data points collected.
The earliest installations of the D’MAND CIRC happened in 2005, and that’s when case studies started being conducted both in-house and by third parties such as utilities, municipalities, and state governments. The beta title was lifted in 2010 after more than 5 years of produce development, testing, and more product improvements.
- The state of California tested the units during 2005 and 2006 by funding a third-party engineering firm to study hot water systems in multifamily buildings. They tested three buildings showing close to 40% savings. Being the earliest tests of this kind, some of the methodology is flawed and a new study was started.
- During this same period, a Stanford dorm tried out the product and reported 20% savings. Also a retirement home installed a unit in one building and did not install it in the other identical buildings. Five years of billing data showed the building with the D’MAND CIRC to consistently use substantially less energy.
- A La Quinta Inn in Duluth, Georgia bought a unit and wrote a letter stating their bills dropped 20% when compared to the previous year. Enovative also did its first in-house case study using data loggers and scientific method to show a building was saving 30% off its bill. This was a 50 unit building in Los Angeles.
- Enovative sent out staff to Washington DC to test a 17 unit and a 34 units multifamily building. The savings were calculated at 15% and the dollar savings where $1,100 and $1,400 per year.
- In 2009, Southern California Gas Company launched a third party program rebating the D’MAND CIRC. Part of the funding was a follow up study on 35 multifamily buildings. The average savings was 1,526 therms per year and 1,236 kWh per year which was an overall reduction of 16%. The table of savings for each building is shown at the end of this document. This data was reported in a 2009 Monitoring Report.
- Enovative also conducted a study on a 6 unit building in San Francisco that also had solar water heating. This building showed a 30% reduction on top of the savings being achieved by the solar energy. ODE Report, Marriott Started, St. Francis Sq., Bluestone
- A customer in New York also conducted his own study and wrote a letter explaining how he tracked his savings of $1,100 a year in water heater savings, but an additional $200 in pump electricity savings.
- Finally, a year long case study at a Marriott Vacation Club resort was started and tracked by Southern California Gas Company.
- The Marriott study was concluding after a year showing a 12% reduction in water heating, which was high considering the Palm Springs climate. The building had 12 rooms.
- Enovative also concluded a study on a similar building, Welk Resorts in San Diego. This was an 8 room building that used electric water heaters so the savings were 18% and over 7000 kWh per year.
- Another customer based in the San Francisco area was lent loggers to track their purchase. They faxed back results showing a 15% reduction in water heating and 97% reduction in pump electricity. This was a 42 unit condo building.
- The continuation of the CA state funded study reported on their new findings, which was based on 32 buildings throughout California. The D’MAND CIRC showed a 15% savings and outperformed all other control measures that were studied.
- A customer in Denver, also tracking their own savings, was able to show a savings of 2,400 therms annually on a 60 unit building.
- Further testing under the rebate program by Southern California Gas showed savings between 20 and 30%, most of these building were small between 8 and 30 units.
- City of Anaheim tested in their City hall and showed savings as high as 50%, but since the system only serviced two break rooms and a bathroom, the resulting payback was still high due to the low hot water consumption.