HTP UTF80 changing min supply temp?
Last Post 07 Mar 2022 04:52 AM by sailawayrb. 4 Replies.
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JerryUser is Offline
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06 Mar 2022 08:17 PM
I have HTP UFT80 boiler on default settings running 2 zones hydronic in ICF house located in CT. I'm thinking to change Min Supply Temp from 86 to 115 or 120 and Max Supply Temp from 180 to 140. Maybe also min outside temp from 5 to -10.

My thermostat is set to 70 at day time and 65 at night although night setting almost never gets triggered becouse it will be morning again and thermostat will switch to 70 deg. Most days heating comes on 2 times in day (24 hr), morning and evening.
My problem is that on warm days with 40+ temp my thermostat will call for heat and supply temp is not hot enough to transfer heat thru the floor and in these instances may take many hours to bring temp up by 1 degree. I feel that by raising min supply temp I will get more comfort quicker and may actually burn less fuel.
Just recently we were returning from trip away and in early afternoon I remotely change thermostat from 65 to 70. 4 hours later when we got home temp was 66 (house didn't feel that cold) as evening hours approach and temp outside dropped house quicker came to expected comfort.

Is there anything I need to take into consideration? Also would these temp be too high to benefit from condensing efficiency?

BTW: I'm using Ecobee thermostats and I can see stats, on colder days my heating runs less then on warm days. On Warm days between 5 to 10 hr per day. On colder days below 6 hours. I do understand that colder days it runs at higher output but on these warm days were runs for long hours I think it will be more efficient to run at little higher rate for shorter time.
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06 Mar 2022 09:45 PM
Unfortunately, one really can't give you any helpful specifics without having the complete building heat loss numbers and the hydronic radiant floor heating design details.

In general, you want to use outdoor temp compensation to vary the hydronic supply water temp such that the hydronic radiant emitter can provide the required building heat gain given the varying heat loss resulting from the varying outdoor temp. The goal is to provide just enough heat gain capability to accomplish this mission across the entire 99% design outdoor temp range without over heating the supply water and needlessly wasting energy and reducing efficiency. So the outdoor compensation parameters need to be tailored to the specific building heat loss numbers and the hydronic radiant floor heating design details. Full disclosure, NextGen Boiler is one of our affiliates. Please see page 14 of this electric NextGen boiler installation manual for an example of these outdoor compensation parameters:

https://nextgenboiler.com/wp-content/uploads/2020/12/NextGen-Boiler-Installation-Manual.pdf

In general, buildings that are more sensitive to outdoor temp variations (e.g., less energy efficient with insignificant interior thermal mass) should use low mass hydronic radiant emitters (e.g., WarmBoard with tile finish) that can more rapidly respond to outdoor temp variations. Buildings that are largely insensitive to outdoor temp variations (e.g., super energy efficient with lots of interior thermal mass) can and should use high mass hydronic radiant emitters (e.g., 5" thick concrete slab). You should never use night time temp setback with a high mass hydronic radiant emitter and likely not even with a low mass emitter either.

As far as maximizing mod con gas boiler efficiency, you typically want the hydronic return temp to be less than 125 degrees F to ensure condensing. A good hydronic radiant floor heating system design typically results in this hydronic return temp being no more than 15-20 degrees F lower than the hydronic supply temp...and specs the PEX circuit diameters, lengths, spacing and flow rates to ensure that this is the case. Everything you need to know about selecting, sizing and keeping a mod con boiler operating at maximum efficiency can be found here:

https://www.greenbuildingadvisor.com/article/sizing-a-modulating-condensing-boiler

And here is a link about your specific mod con gas boiler that may be helpful to you as well:

https://terrylove.com/forums/index.php%3Fthreads/htp-uft-80-set-point.72787/

The suggestions provided in this link are from the same person, Dana, who also wrote the aforementioned Green Building Advisor mod con boiler sizing article. Dana use to participate on this forum, but likely departed because of all the spam and lack of good forum management at the time. Dana certainly knows this subject very well and is a big fan of the HTP UTF80 which can also be purchased from HomeDepot under their brand name. Personally, I am more of an electric boiler or air source-to-water heat pump system advocate when it makes economic sense and when your local grid is largely renewable energy based as it really needs to be. And this is a Green Building forum after all.

I will finish by adding that it is not uncommon for hydronic radiant floor heating systems to be poorly designed which can create precisely these sort of poor performance issues. Many companies simply lack the engineering competence and often just provide a free PEX layout for your floor plan without actually doing any design, much less a proper design, if you buy their products which are also often over-priced.

Gayle
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
JerryUser is Offline
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07 Mar 2022 02:54 AM
Gayle,



Thank you for your reply. I have not read the url you posted but I will.


I understand that there could be many issues and I may not have shared enough information for anyone to be able to help me. I do feel that my issue is not as complex as some may think.
My house is 2 story ICF with 2 zones. Zone 1 (1st floor) has 6 PEX loops and 2nd zone (2nd floor) has 5 loops but only 4 in use. Most of my loops are 300ft and one room has 3 loops of 250 feet. Most are spaced 8 inches a part.



My house may not be the best design but I believe is better then most homes in USA. My house at -9 calls for 33,000 btu. This is why I went with HTP UFT-80, this was on Dana recommendation.

I understand that homes need more heat when temperature outside is cooler as DELTA range is greater, however living in ICF home I do not notice that heat would not come on more with temperature outside being 30 deg vs 10 deg.

I have no explanation for that besides thinking that this is ICF effect and my immediate delta is between inside target temp and ICF temp.
When my house hits target temp in the morning it will take all day before heat comes on in the late afternoon or evening again. However with warm temps outside it take way longer to reach target temp. Typically could run for hours with very little difference in temp change until late evening comes and temperature outside drops and supply temperature increases. Although my basement is not heated on purpose but because this is where boiler and manifolds are it is very warm. I noticed that on couple occasions when I turn heat up the burner didn't even came on because water was at or above target supply temp and just circulates water for awhile before burner kicks in.



Anyway I will read related links you posted and see what I can learn from it.



Lastly I want to add that Dana is great member of this and many other forums and he has teach me and influence me a lot and he should know how important he is to all of us. I'm sure I'm not alone in this. Thank you Dana.
JerryUser is Offline
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07 Mar 2022 03:13 AM
I forgot to say that my system was design to deliver max output of 33,000 btu at 125F.
sailawayrbUser is Offline
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07 Mar 2022 04:52 AM
As a similar reference point, our Southern Oregon remote home is a 2400 sf single level ICF, passive solar heating/cooling, masonry heater, and hydronic radiant floor heating using 5" stamped concrete floor slab emitters with 4" thick under-slab EPS insulation. Our supply temp never exceeds 100 degrees F. We also have lots of interior mass via stone masonry walls, masonry heater, granite counters/window sills, etc. We use a 6kW NextGen boiler (about 21,000 Btu/h)...the smallest they manufacture...and it hardly ever modulates higher than 7,000 Btu/h, the first of its three modulation levels. Plenty of photos on our website if interested.

We never see any variation in our indoor temp from the setpoints of each heating zone...we have seven heating zones. Yes, ICF does have a thermal mass effect which "buffers" the larger peak outdoor temp variations and associated building peak heat loss rates that a heating system would otherwise have to address to maintain indoor temp setpoints. ICF can also create a higher effective R-value than the conventional R-value under certain daily diurnal temp variations. We have a calculator on our website if you want to explore this rabbit hole in more detail for your local climate. But none of this should prevent the hydronic radiant floor heating system from maintaining your desired indoor temp setpoints well.

What are your emitters, concrete slab or something else? Do you use floor temp sensors? These in conjunction with an appropriate thermostat will eliminate any setpoint temp over- or under-shooting. 300 feet may be pushing the limit for 1/2" PEX depending on the building heat gain requirements. We typically stay below 250 feet in our locality to reduce flow rates and resulting head hydraulic friction (i.e., reduce the pumping requirement and associated electrical energy needed). I don’t think any of this is your problem either, but discussing this helps with my thought troubleshooting process. Plus, when I see a potential design deficiency/oversight, I wonder what other design considerations may have been overlooked too.

So it sounds like your system works well when it is colder outside, but it does not work well when it is warmer outside. Could this be because you are not using the correct outdoor temp compensation curve to adjust the supply temp? Ideally, you will want your supply temp to be no more than 125 degrees plus 15 or plus 20 degrees depending on your design at your outdoor design temp. This will keep your return temp at or below 125 degrees F and keep your boiler condensing and efficient across your entire 99% design outdoor temp range. But you also need to select an outdoor temp compensation curve that won't overly reduce the supply temp such that your system can't maintain the setpoint at warmer outdoor temps. I am speculating that you are perhaps using too steep a curve that is causing your supply temp to be too low at the warmer outdoor temps and therefore not providing the required heat gain.

Or maybe you are not even using outdoor temp compensation? In this case you could try setting your maximum supply temp to 125 degrees plus 15 or plus 20 degrees depending on your design. And set your minimum supply temp to the highest temp value below this maximum supply temp value that your boiler will allow (i.e., there is a minimum differential maximum/minimum supply temp a specific boiler will allow). This will work, if as you said your system will provide the full HTP UTF80 33,000 Btu/h at 125 degree F and 33,000 Btu/h or less will also provide the needed heat gain for your actual building heat loss at your 99% outdoor design temp. However, you really should be using outdoor temp compensation to maximize efficiency as I explained in my initial response.

Again, the goal is to keep your return temp at or below 125 degrees F across your entire 99% outdoor temp range...while using a hydronic radiant floor heating system capable of and properly configured to provide only the required minimum heat gain across this entire outdoor temp range. If you have supply/return temp readouts/sensors at your boiler, you can use these to see what is happening and make adjustments as needed to hopefully achieve this goal. But again, without knowing your building heat loss numbers and your hydronic radiant floor heating system design details, I can't say for certain if this is achievable for you. But I suspect it is from what I gathered from you thus far.

Gayle
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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