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MarkS

MarkS

Joined on November 14, 2009

Last Post on August 3, 2014

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The Case for DHW Scheduling

@ August 3, 2014 10:14 AM in A Tankless Coil Experiment

It's well known that a DHW tankless coil is among the least efficient ways of heating water during the non-heating season. We save around 50% on off-season DHW fuel usage by scheduling DHW like you would schedule temperature setbacks for heating. It's just the wife and I, and we both work, so we typically run one DHW cycle in the morning and one in the evening.

We originally did this with an old setback thermostat I had lying around. It doesn't need to be fancy, any 7-day 4-period-per-day thermostat will do. This works if the aquastat switches 24 volts, don't try it if the aquastat switches higher voltages. Wire the R and W terminals in series with the aquastat. Set the On setpoints to the lowest temperature the thermostat allows (ours went down to 40F), and the Off setpoints to the highest (ours went up to 90F). Our basement temps never get below or above those limits, so it worked well for us.

One drawback is how do you get hot water during a scheduled off period. If you only need a nighttime off period this shouldn't be an issue, but if you run extended off periods during like we do, it's beneficial to have an "on-demand" feature to override the thermostat. We did this with a flow switch in the hot water line, wired in parallel with the thermostat so that either the switch or thermostat would create a "call for DHW". It's not instantaneous DHW like a tankless water heater, but for 50% savings we're willing to wait a couple of minutes.

No Contest

@ August 3, 2014 9:39 AM in A Tankless Coil Experiment

If the objective is to compare the tankless coil with a water heater, there's no contest (in the summer). Water heater is the clear winner. Here's a link that lets you compare the operating costs of various DHW systems:

Water Heating Cost Comparison

Output

@ August 1, 2014 5:48 PM in A Tankless Coil Experiment

Interesting question, Chris. In theory, I would expect there'd only be a difference if there's a change in burner efficiency at the lower output, all other factors remaining equal. Even then, it's probably not enough to produce any significant change. But you never know. I'll give it a try the next time She Who Must Be Obeyed is away for a day or two.

A Tankless Coil Experiment

@ August 1, 2014 5:30 PM in A Tankless Coil Experiment

There was a thread in the spring about preparing the boiler for summer where flooding the boiler was discussed. I was curious whether there is any benefit to flooding the boiler when a DHW tankless coil is in use. Since my boiler has a tankless coil temperature sensor and data logging capability, I offered to run a series of tests with the boiler flooded and at normal water level to see if flooding the boiler had any effect on standby losses.

For this experiment, I modified the event logging software to record coil temperature at burner ignition, minimum and maximum coil temperatures, and the time to reach min and max temps.

Test Conditions

- The aquastat cut-in was set to 140 degF
- The firing rate of the boiler was constant at 240 MBH
- The coil temperature was measured by a 10K thermistor affixed to the outlet of the tankless coil

Boiler at Normal Water Level

Five consecutive DHW cycles were observed with the boiler at the normal water level. No DHW was used during the test period. Averages of the five cycles were:

Coil Temperature at Cut-In = 134.2 degF
Peak Coil Temperature = 164.1 degF
Coil Temperature Rise = 29.9 degF
Rise Time = 00:07:59

Burner On Time = 00:02:31
Fuel Usage = 10.1 Mbtu
Standby time = 03:10:03
Standby loss = 9.4 degF / Hour

Boiler Flooded

Five consecutive DHW cycles were observed with the boiler flooded into the risers. No DHW was used during the test period. Averages of the five cycles were:

Coil Temperature at Cut-In = 135.8 degF
Peak Coil Temperature = 158.3 degF
Coil Temperature Rise = 22.5 degF
Rise Time = 10:15

Burner On Time = 00:02:29
Fuel Usage = 9.9 Mbtu
Standby time = 03:17:29
Standby loss= 6.8 degF / Hour

Differences - Normal Water Level versus Flooded

Coil Temperature at Cut-In = 1.7 degF lower
Peak Coil Temperature = 5.8 degF higher
Coil Temperature Rise = 7.4 degF more
Rise Time = 00:02:16 faster

Burner On Time = 00:00:03 shorter
Fuel Usage = 173 btu less
Standby time = 00:07:29 shorter
Standby loss = 2.6 degF / Hour higher

Observations

Standby time and losses are clearly improved with the boiler flooded. I found it interesting that the average burner on times are nearly identical, I was expecting to see longer run times with the boiler flooded due to the greater mass of water. Overall, the on times ranged from a low of 2:28 to a high of 2:35, a difference of about 4%.

More information than you asked for

@ July 16, 2014 7:50 PM in radiator cover box design question

Way back in 1931, the University of Illinois Engineering Experiment Station conducted a study of different kinds of radiator enclosures and their effect on room heating. Very technical, but worth a look if you're interested in the scientific background behind the diagrams Steamhead linked to.

INVESTIGATION OF VARIOUS FACTORS AFFECTING THE HEATING OF ROOMS WITH DIRECT STEAM RADIATORS (1931)

DHW

@ June 23, 2014 11:49 AM in Steam Odyssey 2014

DHW scheduling works just as well as the previous system. Running it off the aquastat for the moment, there's a bug I need to track down that's keeping it from working off of the Phidgets tankless coil temperature sensor.

User Interface

@ June 23, 2014 7:45 AM in Steam Odyssey 2014

The TECO logic controller has a local display, and many configuration and operating functions can be done from there. But I also wanted a PC-based user interface that didn't require me to be in the basement, and data logging capability which the TECO doesn't have. Fortunately, the TECO SG2-20VR model I used supports Modbus, a common industrial protocol used to communicate between logic controllers and PC-based programs/user interfaces.

I kept the general look-and-feel of the user interface from the previous version, and added a few wish-list items. These include real-time/historical trending of most of the analog sensor data, a dedicated trend chart for tuning the pressure controller, and a display of daily btu consumption for each cycle (preheat, heating, hot water). There are also a few "power user" features including a map of all of the data sent from and written to the TECO controller, and the ability to write directly to any coil or register in the TECO.

The software also records system events (burner on/off, boiler cycle changes, state change of switches, etc), daily cycle history (number of times in cycle, cycle time, btu consumption per cycle), and generates a daily log file of analog sensor data. All of these historical files can be viewed in any spreadsheet program.

Screen captures of the user interface:

Steam Odyssey 2014

@ June 23, 2014 7:43 AM in Steam Odyssey 2014

Over the weekend I installed and commissioned the next generation EcoSteam control (dubbed "ES-50") on my Midco LNB burner. The Phidgets-based system that was installed in April 2013 managed the burner control very well last winter, but there were some issues with vendor-supplied software that required the system to be re-started about once a week. I wasn't able to achieve the reliability I'd hoped for, and late last year started looking into a different hardware platform.

For this version, I've migrated the control logic to a TECO SG2-20VR industrial programmable logic relay, which should prove more robust than the Phidgets. Made a few modifications to the control cabinet, installed a new BAPI T10K outdoor temperature transmitter and a Dwyer Magnesense 0-5 inWC differential pressure sensor. Last year I was able to heat the house with the burner modulating to 0.5 ounce of pressure. That's 0.85 inWC on the new sensor. If the pressure setpoint gets any lower I'll have to start measuring it in pascals or millibar. :)

Fortunately, the original control cabinet came with an extra subpanel, so I was able to mount, wire, and test all of the new hardware on the bench without disturbing the existing controls. Even so, there were 50-some wire ends to terminate once the old subpanel was removed and the new one was in place. ChrisJ stopped by for the big day and lent a hand with the wiring. Thanks Chris!

Many of the features of last year's control made it into this one, though a few compromises were necessary. Most important, the outdoor reset strategy hasn't changed. It still uses the heat loss of the building and the heating capacity of the boiler to calculate burner on-time.

One added feature on the new control is the ability to manually fire the burner and adjust the firing rate from the front of the control panel, which is useful for testing and maintenance activities.

The original user interface was running on Windows XP, and since XP support ended in April I replaced the old Dell PC running XP with a low power, fanless PC from Shuttle running Windows 7. In addition to the EcoSteam software, the Shuttle also controls the Insteon lighting in the house.

Here are some pictures of the hardware:

Midco LNB excess air

@ June 20, 2014 12:58 PM in Oil to Gas conversion

It seems to depend on the boiler it's installed in, and what kind of CO numbers you're shooting for.

Last time JStar was out, we ran some experiments with restricting the air intake on the LNB on my Utica. At 20-25% excess air we were seeing CO numbers across the firing range between 2 and 8 ppm. When we reduced the excess air to 12% the CO shot up to 50 ppm while efficiency increased about 1%. I'll sacrifice the small gain in efficiency for the lower CO numbers.

Burner modulation

@ June 14, 2014 3:11 PM in Midco Radiant burner....results of first heating season

Next weekend I'm installing the next generation of modulating control on my Midco. This time around the burner and outdoor reset controls will be in a small PLC with a 0-10V analog output signal. It should be more robust than the current Phidgets-based controls which worked well but required rebooting once a week or so. The new control will still modulate the burner based on boiler pressure. I'll post pics and more once it's in and I get a bit of run time with it.

Valve stem?

@ June 12, 2014 6:20 PM in Name this part

Looks like a valve stem at the very top, but it doesn't make sense that it would be one. I wonder what the screw to the right does (or did or is supposed to do)?

Lab studies

@ June 10, 2014 8:08 PM in Radiators

University of Illinois Engineering Experiment Station, Bulletin No. 223, March 1931. "Investigation of Various Factors Affecting the Heating of Rooms With Direct Steam Radiators"

Download pdf here

Midco

@ May 28, 2014 7:09 AM in Midco Radiant burner....results of first heating season

What did you use for the modulating control?

Tankless

@ April 7, 2014 6:18 AM in how should I prepare the system for summer?

In the summer, that's true, but in the winter hot water from a tankless coil is almost free. Between 10/15/2013 and 3/31/2014 my boiler ran 16 DHW cycles averaging 13.7 MBH each.

In the swing season and summer, our DHW is on a setback schedule. Weekdays it's only active for a couple of hours in the morning and evening. From cold start to shutoff takes about 4 minutes. There's also a flow switch in the DHW line for demand hot water during setback periods. It's not instant DHW like a dedicated tankless, but we're willing to live with waiting a few minutes for the fuel it saves.

I'll experiment with flooding and normal water levels in the boiler after the heating season, and post a report comparing time and fuel usage.

Tankless coil

@ April 6, 2014 1:32 PM in how should I prepare the system for summer?

Can you do this (flood the boiler) if you have a tankless coil that's used during the summer?

Not gold or metallic but

@ March 30, 2014 3:29 PM in radiator paint

during a 2011 remodel we painted four radiators and exposed risers black with Duplicolor engine enamel. Pretty sure we used primer too. After three heating seasons none show any discoloration or paint separation.

Vaporstats and vacuum

@ March 22, 2014 4:57 PM in Vaporstat sticking / biasing after vacuum

When I had a vaporstat on my 1-pipe system, it was adjusted for 3 oz cut-out and -0.3 cut-in. There's a bit of wiggle room in the specs, but probably not for the amount of vacuum you're looking for.

Prior to the rectangular form factor we know today, Honeywell did make a "Type C" Vaporstat with a split-unit range of -10" vacuum to +6 psi (see photo).

Efficiency

@ March 10, 2014 10:01 PM in Boiler efficiency cycling vs continuous run

This thread makes me wish I took more thermodynamics, but even then I don't think it would cover this topic.

I'm a firm advocate against short-cycling, and my first venture into boiler control was to eliminate it on my own system. If you've cut out on pressure (assuming a well-tuned steam system, of course), then make the boiler pause long enough for the latent heat to do its job. Short cycling, in this case, is wasteful.

ChrisJ didn't say "short-cycling" though, so that brings up an entirely different question.

I think what is often left out when discussing steam system efficiency is the time it takes to preheat the pipes before steam gets to the rads. It's left out because in most systems there's no way to tell the difference between preheating and actual heating (when steam is being delivered to the radiators). But the relationship between the preheat time and the heating time is far more indicative of the true efficiency of the system than the boiler rating alone. A 100% efficient boiler is 0% efficient until it's putting steam into radiators. Just ask any "spousal unit".

Example: It takes 10 minutes to preheat the piping, followed by 30 minutes of steam to the radiators. In this case, 25% of the 40 minute overall cycle is "lost". If the boiler is rated 80% efficient, then the true overall efficiency relative to the fuel input is 60% (75% of 80%)

There's a balance point, and it depends on the characteristics of each individual system, where the ratio of preheat time to heating cycle time is lowest. My own experience suggests a preheat to heating cycle ratio of 12.5% to 20% at design temperature, with an outdoor reset system. In swing season, overall efficiency plummets because there's much more time between cycles, with a corresponding increase in preheat times and decrease in heating cycle times.

However you have your system set up, it really comes down to two factors, one objective and the other subjective. How much does it cost ($/btu/degree day/sq ft) and what's the perceived comfort level in the home.

Midco LNB-250 modulating burner firing pics

@ March 9, 2014 10:40 AM in Midco LNB-250 modulating burner firing pics

The Midco guys asked me to take some pictures of the LNB-250 burner from low to high fire. Thought I'd share them here too

Wiring Diagram

@ March 9, 2014 7:55 AM in Thermostats (Honeywell and EcoBee)

Here's a generic wiring diagram. You'll need to adapt it to your particular ignition control. For instance the Honeywell R7184 has a 24 VAC connection so you don't need a separate transformer.

Help or Hurt?

@ March 8, 2014 7:49 AM in For all you steam heads out there

It's hard to tell from the video if they were trying to help the homeowner or screw them over.

Time Delay Relay

@ March 7, 2014 1:42 PM in Thermostats (Honeywell and EcoBee)

Assuming you'll be switching 24 vac through pressure switch, use a Schneider Electric model TDR-SOXP-24. Mouser and Allied Electronics carry them.
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