How to get the best efficiency out of my new boiler.

docbar99 · February 26

I have a new boiler installed recently and just changed the thermostat and I would like to find the best settings in my Hydrostat 3250 Plus. I always keep the thermostat at 63 degrees regardless of the outside temperature. The settings configured by the installer are High 175, low 140 and economy set to 5. ( he told me there was a range of 1-10 and he set it to 5) I later downloaded the manual and see that the setting range is 1-5. I installed a microcontroller to log the data from 4 temperature sensors to both Google sheets and a cell phone app.

The data for the plots below was captured every minute using (4) DS18B20
temperature sensors and one current probe around the Black wire going to the burner. If current flowing, is greater than 0.5 amp, then a digital output = 1, otherwise it is 0. The blue trace is the temperature of the sensor about 6 inches above the circulator. The orange trace is from the sensor on the hot water pipe about 6 feet high.
The third sensor was placed next to the thermostat in the hallway. The forth sensor was located outside of the house near the oil burner.
This is a 3 core boiler with one zone and no separate water heater.

The burner on is represented by the gray trace. There are 2000 readings taken over a period of 1.4 days.
The blue trace is the circulator sensor and the orange sensor is the hot water temperature sensor.

This is the circulator water temperature vs the Burner on / off.

Here is a zoom in of the first 250 readings showing the circulator water temperature vs burner on / off.

In this plot, the inside temperature sensor (Blue) was placed right next to the thermostat. The non-programmable thermostat was set to 63 degrees. The orange trace is the outside temperature which uses the scale on the right side and ranged between 35 and 45 degrees.

Here we have the outside temperature vs the Burner on / off.

This plot is the inside temperature vs the burner on / off.

Here are the statistics based on the 1.4 day test.

hot_rod · February 26

It would be interesting to see the boiler return temperature for a period of time. You want the return to be above the dewpoint of the fuel to dry out the boiler and flue piping. For oil, at least 125 for a few minutes.

A 10 minute run cycle minimum is one rule of thumb, with the boiler return above condensing temperature at the end of the run cycle.

Short run cycles can really drop cycle efficiency

Somewhere I posted the formulas for run cycle and efficiency calculations.

https://forum.heatinghelp.com/discussion/191932/how-efficient-is-my-boiler-no-really?utm_source=community-search&utm_medium=organic-search&utm_term=boiler+run+cycles

HVACNUT · February 26

It looks like the boiler is using a tankless coil, so the Economy setting should be OFF.
So to address the title of the thread, the best efficiency would have been to also install an indirect water heater and get full use of the options the 3250 Plus offers.
Turn off the economy, then make more squiggly lines.

docbar99 · February 27

@hot_rod Thanks for your reply. It the calculations may be a little above my level of understanding. I will try to study and see if I can understand them. I am not trained oil burner guy, just a homeowner. My cycle is definetly less than 10 minutes, so I guess it is a short cycle. Thanks for confirming that. I understand about not going below the dewpoint, but not sure where to measure. If you saw my picture there is one sensor above the circulator and one on the hot water pipe about 6 feet off the ground. In all of the readings I have taken are almost always less than 140 deg.

In spite of the short cycle, the boiler is on only about 12% of the time, so I am not sure how to make it run longer. Originally it was installed at the default settings of Hi=190 with 10 degree differential. At that time I was not monitoring the Burner on signal, but it seemed to be cycling on for a very short time.

Another thing- Since I keep my thermostat on 63 for the heating season, I would assume that it could be another reason for the short cycle. Last year before I got the new burner I had a temperature senson on the baseboard pipe at the end of the run before it went back to the burner and it rarely exceeded 88 degrees.

I just verified my current settings Hi-180, Lo- 140, Eco -5. From what I read in the manual, for a one zone system the ECO should be set to 1 or 2. If you have any suggested settings I will try them.

If it helps- its about a 1000 sq ft ranch house with about 67 ft of 2" in baseboard. If I remember The BTU load is 67 x 600 = 40,200 BTU.

This is the system

docbar99 · February 27

HVACNUT- Thanks for your reply. I am not sure what a tankless coil is, but this is what was installed:

I don't have a seperate hot water heater and I have about 67 ft of 2" baseboard.

I just verified my current settings Hi-180, Lo- 140, Eco -5. The switch is set in the indirect position. From what I read in the manual, for a one zone system the ECO should be set to 1 or 2. If you have any suggested settings I will try them.

hot_rod · February 27

1000 square feet of total heated space? I would expect a heatload of 30,000 at the most 35,000 btu per hr on design (coldest) day. If the home is energy efficient the load could be in the 20,000 range.

67 feet of fin tube at 180 supply is more like 550x 67=36,850. So that would be close to the high “guesstimate”.

If so the boiler is about twice the size you need, 65,000 net output. So short cycling is going to be a concern. Is it all on one zone, one thermostat?

There are some free online heat load calculators, fairly simple to use.

One in the Burnham Heating Helper.
Uponor CDAM manual is a free download with a load calc.

Does the boiler also generate the hot water, the black cover in the left? Or is there a separate indirect tank?

https://www.usboiler.net/digital-heating-toolbox.html

https://www.uponor.com/getmedia/af0b8e90-a8f2-4b9f-803c-56cb08864302/cdam-chapter-7-heat-loss-considerations-and-calculations.pdf?sitename=USA

docbar99 · February 27

Thank you again for a quick response. Yes- it is a one zone system with no indirect storage tank. I remember that while shopping for a contractor I was reading up on heat loss calculations and boiler sizing, but did not understand it fully and none of the contractors I called thought it was necessary to do a heat loss analysis. The contractor I hired thought I should go with the same model that I already had. I knew it was oversized based on my calculations, but did not trust my calculations. I agreed to the same boiler but asked for the Relilio boiler because it could come with a 0.6 GPH flow rate.

I guess I have to expect some short cycling, but have a few questions.
1- The switch on my hydrostat is down (indirect position) is that right?

2- I would like to do the best settings possible in spite of the boiler being oversized. With the settings I have now, the measured temperature is 63 deg + / - 0.5 as measured by the sensor right next to the thermostat. It's not exactly toasty, but nobody is home most of the day and I prefer to leave it at 63 as that is a good sleeping temperature.

Would it make sense to adjust the differential on the thermostat from 1 to 3, to reduce the short cycling ?

3- Since the water temperature is mostly on the low side, would it be good to set the Circulator Hold Off (Enhanced Condensing Protection)?

Looks like the temperature near my circulator pump goes all the way down to 80.

4- It seems that the short cycle while usually considered undesirable, my burner is only 12% of the time, what am I really trying to fix? ( I know, the outside temperature was 38 degrees on average during the 1.4 day test)

5- I suppose my baseboards will have a better heat transfer with a higher temperature, but that may result in further short cycling. Any settings I should try?

hot_rod · February 27

Spread the on off differential out to 30 if you can. The anti condensation function of holding the pump off may help, of it could cause more issues on mild days,

so you have two sort of related issues, over sized boiler and the short cycling caused by it, keeping the boiler running cold.

A buffer tank would help, but there is some $$ involved.

You could do the number crunching I mentioned to see how much the boiler is over sized

Heat load calculation, then with the data logger calculate the efficiency based on the run time vs the the boiler size. You have most of the data except an accurate load calculation

HVACNUT · February 27

docbar99 said:

HVACNUT- Thanks for your reply. I am not sure what a tankless coil is, but this is what was installed: I don't have a seperate hot water heater and I have about 67 ft of 2" baseboard. I just verified my current settings Hi-180, Lo- 140, Eco -5. The switch is set in the indirect position. From what I read in the manual, for a one zone system the ECO should be set to 1 or 2. If you have any suggested settings I will try them.

To get the firing rate you show, the burner Must be the Riello F3.
The tankless coil is the black circle on the front of the boiler with the pipes and Hydrostat coming out of it. It's what makes your domestic hot water.
When using a tankless coil with the 3250 Plus, the economy setting should be set to OFF.
The number of economy settings roughly corresponds to the number of heating zones. You have 1 zone. So even if economy were used, that's were it would be set. But again, you have a coil so economy is off. It's in the manual.
And switch the Z/I switch to Z, because you do not have an indirect.

hot_rod · February 27

Here is what a tankless coil us, and how it slips into a boiler
So cold water enters the copper coil and is heated by the boiler water surrounding is

As such, your boiler needs to remain hot, always.

Its not the best way to generate dhw if efficiency us a goal

It could also be a reason the boiler size is larger than the heat load to provide adequate hot water

docbar99 · February 27

Hi Bob- Thanks for your advice, you guys are amazing, always willing to help. I will change the settings and try to work out the load calculation.

docbar99 · February 27

HVACNUT- Thank you for your continued support, much appreciated. Yes- I did request the Riello with the small nozzle. Of course I have no way of verifying the nozzle size. I am glad you explained about the tankless coil, because I was confused about that. In the Hydrostat manual wiring section they have wiring diagrams for HEATING and Indirect Water Heater or HEATING ONLY – No Indirect Water Heater.

Sorry for asking so many questions, but if I change the switch from Indirect to Zone, do I need to switch the wires from B1 & B2 to ZC & ZR ?

HVACNUT · February 28

docbar99 said:

Sorry for asking so many questions, but if I change the switch from Indirect to Zone, do I need to switch the wires from B1 & B2 to ZC & ZR ?

No. B1,B2 is power to the burner. ZR,ZC is only used with additional zones or indirect.

docbar99 · February 28

You guys are giving me an education in hydronics. I am 67 now and when I was 20 I was interested in the oil burner course at BOCES trade school. I was planning to enter that field, Instead I wound up joining the air force. I am getting interested again. The support on this site is amazing, I have never had tech support this good even from companies that I have purchsed product from. Thanks again, I will post results when I get some.

docbar99 · February 28

OK, so based on the suggestions I got from this post I mad the changes this morning. First was changing the switch from Indirect to Zone. Next HH left at 180, LL to OFF, ECO to OFF. Set Diff to 30 deg.
This is where I am not sure if I did something wrong...... I was not sure how to exit Program mode after setting 30. Eventually I turned the LL adj. and it seemed to exit the mode. I then checked settings with the test button .....HL=180, LL= OFF, ECO = OFF.

Then after taking a shower I went down to take a look and saw that the temp reading on the Hydrostat was reading 130 and the burner was still off. I thought that at 150 it should have turned on, so I manually set the LL to 140. The burner turned on and then I then left for work. When I got to work, I checked saw that the burner only stayed on for about 2 minutes.

Its in the 50's this morning, and the burner stayed off until 9:30 AM.

Then the burner stayed on for 10 Minutes.
This image does not show that because it shows only up to 9:05.

If did something wrong in the programming, please let me know.

HVACNUT · February 28

Because the boiler has a tankless coil, the boiler must always maintain a minimum (Low) temperature (typically 20° below the High Limit setting) so you have domestic hot water. With Low off, the only time the burner will ever come on is if TT closes on a heat demand.
Drop the High to 160°. Set the Low to 140°. See how that works for you. You can always raise them if needed, keeping 20° between the two.
So now with a heat demand, the burner will run until water temperature reaches 160°, or the heat demand satisfies. If during the heat demand the boiler temperature drops below 140°, the circulator will shut off so the boiler can heat up again. The reason being, if the boiler temperature continues to drop and you're in the middle of a shower, it's gonna be a cold shower right quick. Once the Low Limit meets the differential, it will turn the circulator back on.

This diagram is not from Hydrolevel but it shows the general function of the triple acting aquastat, which is what yours is being set up as. The Hydrostat has 10° fixed differentials.
With these settings, the boiler will always maintain 140°, dropping to 130° before powering the burner to make 140° again. The draft regulator has a lot to do with the time it takes between firing. You don't want the heat getting sucked out of the boiler while the burner is idle.

docbar99 · February 28

@hot_rod- Thanks for the detailed description of the cycle. That makes allot of sense. I think it is working pretty good now with HL=180, LL=140, ECO=OFF. I thought someone in the thread had suggested, setting LL= OFF, but looking back, I saw that in the manual as the default setting. I thought that if it was set to OFF, it would switch at the HL- DIFF, which was set to 30. But when I saw the temp dropped to 130 and the burner was still off, so I set the Low to 140. Once this run of 2000 measurements is complete I will try setting the HL to 160 as you recommended. But for a short test this looks like its better already I am seeing the burner stay on for 10 minutes so far. This is what the first 500 readings look like.

Is it always necessary to remove the Jumper when you adjust LL?

Thanks again!

EdTheHeaterMan · February 29

When someone suggests that your boiler is too big, they are probably correct, but they fail to mention that there are no boiler manufacturer that offer a 20,000 or 30,000 BTU per hour input oil fired boiler. Add to this the fact that you are depending on this boiler to make Domestic Hot Water from that tankless coil. That is basically an on demand water heater that will need at least 84,000 BTUh input to maintain the 3 Gallon Per Minute temperature rise of 60°to 70° temperature rise needed for taking a shower that will last more than 30 seconds.

You have the smallest boiler available from that particular manufacturer. And I don't know of any boiler with DHW Tankless coil that has a firing rate below 84,000 BTUh. You have the right boiler based on your situation. The only thing you need to do is to make the necessary adjustments to get the short cycles that will happen to be as long as possible by increasing the differential to the max setting. One other thing that can increase the cycle rate is a buffer tank that will keep the burner on for a longer time and off for a longer time. It is kind of a flywheel effect where the burner operates longer because there is more volume in the system so it takes longer to heat up, and likewise it will take longer for the system to wind down from that high temperature.

docbar99 · February 29

Thank you Ed. You have already assisted me with the re-wiring of this boiler and I appreciate your input. I was aware that the boiler was oversized for the house and that is why I requested the Riello burner to get the 0.6 GPH flow rate. I had a not so great installation and with the help of awesome members of this forum I have been correcting some of the wrong settings that were configured by the contractor. Some settings I tried yesterday increased the boiler run time from about 3 minutes to about 10 minutes. I know having an Indirect hot water heater would improve the overall efficiency, I can't make that investment right now.

How to get the best efficiency out of my new boiler.

Comments

Categories