The sun is telling us to stop

As the season progresses, the sun rises more and more in the East and even to the North of East.  That means it’s beginning to strike and warm up the outdoor air temperature sensor on the East wall of the building (shaded from low winter sun by a hillside and by an entryway to the South).  No problem in the winter, but look what it does in May!  (Times are shown on the x-axis at the bottom of the figure.  The temperatures on the y-axes are shown in °F.)

It’s time to turn things off–this time hopefully till Fall.

…or not!

Given the cold weather last night and possible frost expected the next two nights, I went over to the school this morning, shut some windows and turned the heat back on.

It’s tricky providing heat in this season since it often gets warm enough later in the day that windows are opened up.  If no one closes them in the afternoon, then heating up the building in the morning is a bit difficult and just a bit wasteful…  The next few days are not expected to be that warm even during the day.  We’ll see how it goes.

First Heating Season Complete!

The decision a few days ago to turn off the heat to the school marks the close of a successful first year.  We beat our target BTU consumption by 3%, which is not earth-shattering, but quite respectable for a first year where there were a number of kinks to work out with the system.

We’re proud to say that not one of these kinks in the boiler plant was noticed by people at school—we caught them all with our monitoring system and remedied them before any complaints occurred.  There were some misunderstandings about how to use the thermostats to keep comfortable.  If you read further, you’ll see why!

The total fuel consumption was:

  • ~35 tons of pellets (target = 36.5 tons)
  • 57 gallons of oil (target = 27 gallons)

What is most encouraging about this performance is that virtually all of the oil consumption was due to events where the oil boilers kicked in too soon—essentially mistakes.  The logic governing the operation of these boilers has been adjusted to keep these backups from coming on unnecessarily.  This is terrific since it means that our pellet boiler (nominally 200 kbtu/hr output) was able to maintain temperatures in the building as well as the failed 450 kbtu/hr boiler it replaced.

There was a period in January where the pellet boiler ran 24×7 (other than to fill and clean itself) to keep up with the sub-zero temperatures.  Even with such a severe test, it functioned very well and kept the school warm.  If we had a higher output capacity, we could afford to set back temperatures at night in the coldest weather (thereby saving energy), because the greater output would enable an effective recovery to comfortable temperatures in the morning.  We chose to use the pellet system steadily (lower output and cheaper fuel) rather than the drawing on the extra oil boiler output capacity to enable setback.  This was because we wanted to minimize costs rather than overall fuel consumption.  In the less severe weather, we certainly did set temperatures back at night, but provided sufficient time for the pellet boiler to reheat the building in the morning.

What’s next?

  • A portion of the building has been found to be very poorly air sealed.  Unfortunately, that means that the radiators installed cannot keep up with the heating needs in colder weather.  It is not an issue of insufficient boiler output, but rather a mismatch between the pre-existing distribution system and the heat loads.  We intend to explore options to remedy the severe heat loss.  (The excessive heat loss leads to real comfort problems.)
  • Additional problems need to be addressed with the building’s control system.  Most existing thermostats are not digital and are not calibrated!  A thermostat set to 58F may heat a space to 75F!  Certainly some savings are easily achievable here.  We’re looking into solutions that would wrap the control of the distribution system into our control of the boiler room.  If these systems operate in a coordinated way, major comfort and savings improvements can be achieved.
  • There have been some problems with the load cells (essentially scales) for the outdoor pellet storage bin.  We’re planning to use the off season to remedy that problem and obtain a much more accurate picture of fuel consumption in between fillings.

As hard as it may be to imagine now with this beautiful spring weather, we’re looking forward to the next heating season to see how much we can improve.

What’s happening at MWS?

Sometimes no news actually is good news!

We had a very smooth month of December, with very few issues.  Careful monitoring of system performance during the first few months of operation led to several upgrades in the control strategy, some of which were made at the end of 2012.  Broadly speaking, we’re always looking for ways to smooth out and extend the pellet boiler operation and minimize the use of the oil backup.

We’re pleased to report that the oil boilers have used a total of 7 gallons of oil from day 1, the bulk consumed during initial tune-up and system testing.  The remainder of the usage actually occurred during times when the pellet boiler could have kept up with the building’s requirement for heat.  In other words, this operation was a mistake that has now been corrected in the control algorithms.  We find unnecessary use of backup boilers to be both very common in other installations and easily preventable if you’re interested in doing something about it.  Why not use the renewable energy system as much as possible?

The photo at left shows the cumulative ash cleaned out of the system as of December 31. Not bad for nearly 13 tons of pellets!  The crew doing the boiler maintenance and cleaning reported that the quality of the ash is exceptional, and that it represents a very clean and efficient burn.  (Never mind that this crew was from Froling Energy!  However, they see many other boilers requiring cleaning/maintenance and have ample exposure on which to base a comparison.)

Another encouraging point of comparison between Xylogen’s operation of this pellet boiler and the operation of other, identical pellet boilers elsewhere is that we have a very low number of boiler starts—around 500.  This is easily half or even one-third the amount typically seen in other boilers at this stage in the heating season.  Why does this matter?  The fewer times the boiler starts, the less wear and tear it experiences.  Also, the startup is the least efficient portion of the entire combustion cycle.  We’re doing pretty well here, but have just instituted some changes to do even better.

The original 13 tons in the external pellet storage bin were nearly depleted on January 2, when a small delivery was scheduled.  The delivery allowed us to buy a little time to make a few adjustments to the bin before it is fully refilled.  The load cells will be adjusted to provide us a more accurate measure of the rate at which the pellets are being consumed.

Based on previous consumption records, we estimated that it would require about 36.5 tons of pellets in a typical year to satisfy the heating requirements at the school.  We’re approximately one-third of the way through this amount and obviously eager to do better than the projection!

With that goal in mind, we obtained permission from the school to reduce the space temperatures during the recent vacation, allowing us to conserve some fuel.  No point in heating an empty building to normal levels!

We’ll keep you posted with more updates as the heating season progresses.  Feel free to send us questions or comments (below, or by email).

Ash Collection

Yes, this is an unusual view—gazing straight into the tr/ash can.  What you see here is the accumulated ash from two months of operation.  Not much.  This is a 21-gallon can, and you can see from the lower photo that the bottom is filled somewhere between 5 and 6″.

As we get into the colder part of the winter, this will fill faster, but it is still rather remarkable how little waste there is when burning premium wood pellets with this equipment.

Of course, this can’t even be considered waste, as it can serve as wonderful fertilizer for plants.

Hmm…

(http://icanhas.cheezburger.com)

You’ll see why this is relevant in a minute…

 

Much to my chagrin, I saw that the fuel consumption for the school was greater on the Thanksgiving holiday than on the preceding days.  Something must be terribly wrong–or is it?

During non-school hours, we set back (lower) the temperature of the school to conserve energy.  We cannot make extreme setbacks since the masonry building takes a great deal of heat to warm up in a reasonable time.  (To control costs, we need to ensure that the pellet system is capable of providing 100% of the recovery from setback.  We could choose to have a deeper, more aggressive setback and save more energy, but we’d have to enlist the oil boilers to recover from the setback.  That would save energy, but would be more costly.)

So, on Thanksgiving, the temperature was set back all day.  You’d expect some nice savings relative to the preceding day–or at least I did, till I thought it through.  So what’s the deal?

Students!  The children (and adults) at school generate a lot of heat when they’re there.  And since this is no sedentary school, they generate lots of heat.  With a few assumptions, the occupants of the school generate about 55 kBtu/hr of heat.  For some perspective, the pellet boiler generates 200+ kBtu/hr of heat.  If you assume the school is full for 7 hours of the day, people are displacing about 57 pounds of pellets each day!

(Lights are another contributor as well.  If I get around to it, I’ll estimate their contribution.)

Putting it all together, we saved pellets by lowering the temperature setting, but we had to use more pellets since there were no people and no lights contributing heat to the building.  We’ll continue to experiment with the setbacks while still permitting a reasonable recovery time using pellets alone.  It certainly seems a reasonable goal to use less energy when the school’s empty!

Maybe we should add some more students to reduce our fuel costs…  (I hope the cartoon now makes sense!)

We see the big picture, too

Yes, we can create a mean boiler room, but that’s not the extent of our ambition.  Our goal is to find creative ways to conserve energy for our customers and to wring every bit of utility out of the fuel that must be consumed.

The assembly room at MWS has been notoriously difficult to keep comfortable.  We didn’t make any changes to the distribution system at the school (just the boiler room), so this is a problem we inherited.  Regardless, it reflects poorly on us if the “top-notch heating system” doesn’t keep the space comfortable…

So what’s going on?

  1. The rim/band joists and sill plate under the entire room are poorly air sealed, so the dropped ceiling cavity below the floor is bathed in cold air from the outside.  Never mind that this is where all the heating pipes run…  This creates an uncomfortable variation on radiant floor heating.  We would like to explore options for retrofitting the perimeter with spray-in-place foam insulation to stop this infiltration of cold air.  That will improve comfort and energy consumption upstairs and downstairs.
  2. A single, very long loop of baseboard radiators was installed, much longer than any others in the school.  Flow rates are likely poor through the loop (this can be confirmed with a simple delta-T measurement–yet to be done).
  3. Mattresses and other items were stored over the radiators, preventing the heat from escaping from the radiators to the room.  This is a simple fix.  (Hint: don’t put a sweater (or bed or couch or furniture) on your radiator!  It ends up heating the exterior wall and the outside air rather than your room.)
  4. When looking at the room on Monday, I noticed a distinctly frigid blast of air emanating from one of the grilles in the ceiling.  This grille is associated with an exhaust fan that’s never used due to unacceptable noise.  I guess there’s no backdraft damper…  I sealed off the grilles (there were two) and left with high hopes.

When I went in Tuesday morning, the temperature in the room was at the thermostat setting!  This was the first time I’ve ever seen it satisfied first thing in the morning.  A few pieces of paper and some scotch tape–pretty high-tech, isn’t it?!

It gets even better.

Monday and Tuesday were equally cold (as measured by heating degree days).  Our daily fuel consumption dropped 12% from Monday (grilles open) to Tuesday (grilles shut).  Yes, there may have been other things going on, including slight variations in the daily topping off of the fuel bin, but even 5% improvement for such a simple fix would be terrific.  And the space might actually become comfortable!

Today, an opening to an old ventilation shaft was discovered and promptly covered over.  Heated air was escaping the building through the grating at such a clip that a small student might have gotten sucked in and trapped on it!  You get the picture…

Also, there was an assembly today in the assembly room (makes sense!), so we decided to turn down the heat in advance to try to avoid overheating and waste.  It turns out the audience itself raised the temperature at least 6F.  Good thing we didn’t start out toasty.

Small, very simple steps can have a big impact.  We’re looking at the high tech, the low tech, and everything in between to make a difference.