Help with heat loss and finishing existing design details_1

Mike Krall

We've got a house with a heat loss calculation and tube plan done (old Wirsbo - 2002). The tubes are in the radiant panel floors.

There is a heating system and control design from a very experienced hydronic designer. The designer did the work out of interest, goodwill and kindness... did as much as there was time for, and did more than there was time for.

I know the designer had all the bits and pieces figured and understood. What I truly understood at the time, and now, years later, is a lot less than that.

I can't talk with the designer and there is no one around here that understands why the design is as it is. That is, the plumbers look at the design and say, "We wouldn't do it that way". I don't know a lot, but I do know they do not see how it works... why it works... why what they would do (and I asked) won't work as well as it could.

I think there are two parts to this:

1) Find out if the heat-loss calculation needs to be redone.

2) Based on above, validate boiler size, DHW indirect size, then fill in the blanks I have with the existing design.

So... one thing at a time...

Heat-loss calculation:

I've gone over all the back and forth with the designer... e-mails and call notes. I've re-read years of collected links and papers pertaining. I've read a lot more pages in the Caleffi Idronics Technical Magazine issues now, and done searches on, and read "The Wall")... weeks of all the above.

I've come to wonder if the Wirsbo heat loss calculation is correct... or correct enough. I don't have any way of knowing.

These factors:

* Total interior sq.ft. is 1.4% less than Wirsbo calculated on... 1750, not 1776

* Wall ht. not 9 ft.... 946 sq.ft. 1.4% less... 804 sq.ft. is 7.6% less than 9 ft. of Wirsbo calculation.

* All exterior wall is 8" lt.wt. concrete block with sand cement (6-bag) core fill... 3" XPS on outside,
with 3/4" stucco exterior and interior... very high amount of non-emitter mass.

* 91 feet of interior wall 8" lt.wt. block with filled cores... 36 feet interior frame wall with 7/8" stucco each side.

* South facing windows 6.5% of total floor area. In the books that is 0.5% below "solar tempering"... i.e., an amount of gain a 'normal' furnished stick house has enough mass to take up and hold.

* Floor 4" concrete... 1/2" sand... 2 1/4" extruded brick laid tight. 2" XPS under and at edge (with block stem wall and 3" XPS outside of that. PEX centered in concrete... (230 sq.ft. of total floor concrete or tiled concrete)... all piped slab meeting interior block wall with 2" XPS at edges.

* House is partially bermed... floor levels at 3" above grade to 2 1/2 feet below grade... most floor edge is below grade.

* Wirsbo used -15 Degree Day temp. We are 7 miles from KLND (LND) and the 99% heating is -6 to -7 (depending on report year... but I really don't know if I looked at the right thing, and I might not have understood what I looked at).
I can say, we are 500 ft. higher elevation than KLND (5587 ft.) at the base of the Rocky Mountains. Upshot of that is, we are above the valley's winter thermal inversions and KLND is not. Our normal is +5 F KLND in the winter... the cold slides down and away from us.

The house was built to be tight... all exterior penetrations foamed in... good U-value windows... sheet rock ceiling sealed at edges prior to mudding, with low perm. primer and paint... all ceiling and wall penetrations foamed shut... R-44 cellulose ceiling insulation laps over exterior walls and it's XPS/stucco. Not close to modern "Super Insulated/Supertight", but...

* Wirsbo used 0.35 for infiltration calculation.
-----------------------------------------------------------------------------

That is WAY more yapping than I wanted....

The question is... does the above look like a decent fit with a calculated 37,460 Btu/hr design day loss?

If the answer is no... I'd like to find someone who (on a pay-for-the-work basis) has experience with this kind of house oddness and would like to mess with figuring it's heat loss out.

Mike

hot_rod

around 2809?sq ft at a -15 design?  Seems reasonable at 20 btu/ sw ft. A bit high maybe because of the -15 design. About the smallest boiler you will find is 50,000 input, so it would modulate around that load nicely

The next step is assuring there is enough tube to move that amount of btu/ hr

GroundUp

Unless you're going with an electric boiler, it doesn't really matter as much as you may think. You don't mention the insulation values of the walls, but if it's simply core filled CMU with no insulation, I'd say your calc is quite low

EBEBRATT-Ed

If it was installed in 2002 the question is how has it heated for the last 20 years?

I think you are way overthinking this.

A heat loss will never be an exact #.

Have 20 different people do a heat loss you will get 20 different #s

You're just looking for a safe range to be in

Mike Krall

@hot_rod @GroundUp

I misled via 'too much data and not enough description'... 1750 sq.ft.... 37460 Btu/hr design day / 1750 = 21.4 Btu/hr/sf.

3 inch XPS outside 8 in. cement-filled core, lt.wt. block... cement stucco both sides... Approx. functional R-value of 23-ish (From a long time ago in a now-lost source, a consideration of the mass (effect on U-value and/or Delta-T... or some such))

NOT disagreeing 'Hot Rod'... I do understand the reference to minimum available mod/con boiler size.

My question on correctness of heat-loss calc. comes from not knowing anything about how likely Wirsbo understood this building in 2002. They did have the description of it.

Other factors being generally acknowledged:

* Heat-loss calc. 'padding': 10% - 25% range... various sources
* This: https://web.ornl.gov/sci/buildings/conf-archive/2013%20B12%20papers/165_Saldanha.pdf
* @Mark Eatherton off and on and adamantly on the topic of high levels of non-emitter mass. My read of "ME" being... the effect is there and it is notable enough to consider... but it is not considered.

My KTE (kitchen table engineer) calculation is: minus 5% for -15 to -7 degree day difference... minus 10% HL calc. overage... minus 7.5% (pulled at relative random from above link).... Makes it 29k Btu/hr. Am I at all close? Doesn't matter anyhow... except maybe as leeway... or as a thing to understand how much of a heating season will be below modulation limit. Stuff like this means something to me, though
----------------------------------------------------------
So... House with two halves... north and south. Dividing point is 6 inch drop north to south... two clear-to-the-ceiling openings of 6 ft. and 5 ft. (Cold air dropping drives passive air movement.)

South 1/2: 946 sq.ft.... remote manifold... 4 loops - 954 ft. total - 40 ft. under cabinets (loops equalized when laid ... 238.5 ft./loop - +/- 2.5 ft.... All open... long side "L" is south wall

North 1/2: 804 sq.ft.... remote manifold... 4 loops... 834 ft. total - two longest loops equalized near 220 ft (east and west bed rm.) Entry/Ut. Rm. loop approx 213 ft.... Bath rm. 181 ft.... 11ft. under bath tub... 5 ft. under vanity... 11 ft. and 36 ft. in closets (louver doors).

Wirsbo calc. 87.7 deg. water in south 1/2... averaged out 87.3 deg. water north half... with -10 deg. at surface both halves.

Mike

Hot_water_fan

If you have 20 years of experience living with the system, then I wouldn’t overthink it. Easiest method would be to look at how much fuel you used. 

Mike Krall

@EBEBRATT-Ed @Hot_water_fan

Didn't say clearly there is a house with tubes in the floor and a design on a piece of paper for building a system to heat it. I knew that was the case, but I didn't get you to know it. I'm sorry I did that.

Mike

Mike Krall

Any other ideas?

Where next, would you say?

Mike

hot_rod

I think the load number is pretty close. Certainly close enough. The load calc is only as good as the inputs. And at that it is just a point in time, the load can change minute by minute. Without someone doing a complete detailed load calc, maybe with a blower door number to pin down infiltration, I'm not sure what else you can do?

Mike Krall

Thank you for the response, Hot Rod.

I'm very sure Wirsbo's view of inputs is a lot better than mine would ever be. I was never "needing" to re-do the heat loss calculation. I was wondering if anyone here felt it should be... mostly in view of the very high mass w/ small amount of solar-gain. I also have no doubts on Wirsbo's tubing layout and water temp. calculations either. And I do understand every system will need to be wiggled for a tighter fit when up and running, anyhow.

Right now I don't know how to start into the rest of this... to get the existing design finished in the manner I need... that I understand the details... the how's and why's. I need to get organized. That will take me a bit.

I should ask... I have a copy of the design as a .png, but could make it .jpg, or other. What is a more ideal format for the forum structure and member use?

Mike Krall

Jamie Hall

The high mass will only affect you in one way: response to requested temperature changes will be slow. It does not affect the heat loss. The small amount of solar gain (pity -- it works well with high mass) -- simply means that you won't have any appreciable help from the sun -- and again, doesn't affect the heat loss (think night time) much.

Mike Krall

Jamie Hall...

Do I understand?

This building, this mass (very high level of emitter and non-emitter), this depth of tubing, this solar-gain (approx. 15%-20% "Solar Savings Fraction"), this infiltration, this design day heat-loss. Due to the high mass alone, any heating-system-required internal temperature change (+ or -) involves a change in all the mass, and that takes a significant amount of time?

Mike Krall

I'll tell you a small story...

The winter I put the brick floor in (the house was unheated), there were no frame walls (as few as there are) and natural air flow was maximized via larger area to area openings. There was a three day time period with a heat-of-the-day high of 10 deg. F the third day... nights to -10, -15, -5. It was totally cloudy those three daylight periods... could not even see the disc of the sun in the clouds at any time I looked. The temperature in the house had wobbled a little around 52 deg. F. the three days. 48 hours later in the afternoon (two full-sun with snow-covered ground days, and notably higher diurnal temps), the house temperature bottomed at 47 deg. F.

OK... no more stories.

Hot_water_fan

Mike - mass doesn’t change the heat loss. It will be slower to respond to temperature changes. 

Mike Krall

Preamble:

I feel this may be complicated. I feel like I'm going to be asking for a lot of help.

I have to say this again.

If anywhere along in this you-all feel like the best way to continue is for me to work with (pay) a designer as opposed to continuing on The Wall, please say so. If doing that is the better way, I'll need to find someone who wants to mess with this, and I would appreciate help finding that person.
---------------------------------------

The attached system design is not a final design. That didn't happen in diagram-form because it didn't need to at the time. There were "in progress" modifications via e-mail and phone call with the designer.

My last few phone calls with the designer were to finalize all the component details and for me to come to an understanding of control logic and process. The designer knew exactly. I did not understand exactly... and took lame notes. What I have for some of the design now are my impressions and the cryptic notes.

The designer's evolved intent was very specific to elegance and simplicity... that this system would run quite well without whistles, bells, automatic water feed, auto WWSD, and more.

I'd like to continue on that road... BUT... there are 9 (+ more) years between then and now, and the world is not exactly the same. AND... I learned a very long time ago, when a person asks advice from someone(s) who knows their business and what the job is... to take the advice and help given, then say thank you.

I Do need to understand all the pieces and interactions of the design. I feel it's the only way to get it built as it needs built... and then, I Am going to have to understand it to run it. Also, I do not want to (Will Not!) work with the plumbers on a "do what you are told" basis. In my first post, I said "they wouldn't do it this way". Their view is: Air thermostat call to on/off zone pumps (I assume using ODR, but I didn't think to ask). I feel certain this design shouldn't be that way... that constant circulation as a base is required. In the end, I want to be able to say, and show, the plumbers what a thing is, how it fits, and why. They have said, "We'll build whatever you want". I'd like to be able to show them one of the other ways.
---------------

From the design drawing:

*** The boiler shown on the "Piping Diagram" had evolved into a Lochinvar Knight WHB085L (LPG). This looks like "too big"against a 37.5k heat loss. The designer said, "I have to be able to make you hot water", and some other things I don't remember related to the boiler size. I felt that had to do with the time off from heating with a Lochinvar SIT040 indirect on priority... that there were times when hot water was being made that were not good times for the heating to be off (Maybe a solar-gain aspect? or ???). The intention was the water heating would be scheduled... on some to-be-determined schedule... gotten done quickly and right back to heating.

_ Feb. 2022 Lochinvar Knight brochure: 55k w/ 8.3k min.... 85k w/ 8.5k min. The 55k has a 6.63 : 1 turn-down ratio... not 10 : 1, as the 85k has.
Just to say... The plumbers use Lochinvar (primarily for commercial work) and Navien (most of their residential work). The plumbers recommend Navien for this job. The designer was very happy with Lochinvar... others were mentioned, but not Navien.

_ The designer's idea was to have all pumps the same... Older Lochinvars came with Grundfos UPS15-58. All diagrammed pumps were to have integral FC, even though the constant circulation pumps didn't need them... made for an easy spare parts list.

_ On current Lochinvar site, a .pdf with current boiler pump as Grundfos UPML 25-104. (There is a possibility the document was a European version.)

_ Very low hot water usage... on Lochinvar SIT sizing work sheet, our total = 60 "1st hour rating" (pg. 16, SIT I&O).

_ The designer pointed to a Lochinvar SIT 040 indirect as it has a lower per-hour loss rate than a SIT 030 (0.9 deg, vs 1.5 deg.). With the intended, scheduled, DHW making I'm guessing at a larger tank also carrying the off-schedule time better... and (from Robert O'brien) charging to higher temp. (guessing min. 140F - 160F) makes it a "bigger" tank that will also pass time better. I do know it needs a mixing valve for < 120F delivery.

_ The DHW indirect HX flow direction is different than many piping diagrams I see. I don't know what (unless it's a "late night mistake") the higher good in doing it that way is. I can Guess at some kind of heat exchanger counter-flow, but ???

_ The LLH is purchased. The designer had designed one and we were going to build it here in town... approx. 4 gal. Building it here fell through. The designer ran into a deal on a Viessmann 120/80 that was felt to suffice, though 1/2 the volume of the designed LLH.

_ Remote manifolds 26 ft. and 32 ft. from boiler wall... down, under floor structure, then up via PVC pipe (been tested and 1" PEX goes through). Diagram may be showing the 1" feed to remote-manifolds as "up, over, and down"... again... 4 loops each manifold... 1/2" oxygen-barrier Rehau.

_ Designer's ideal was 1 1/4" body-dia. manifolds ("T"- drill) but the plumbers can't make them. 1" Watts SS or equivalent was fine with designer... some type with shut off - purge - air vent - thermostat was the view.

_ I mentioned in an early post, the designer felt running the same temp. water in both zones was the correct way to go. There was a discussion on potential temp. differences in north zone rooms given unequal loop lengths. The idea of manifold flow adjusters did not come up. We were both thinking the two longer loops (close to equal) would be cooler... the shortest loop (bathroom) would be warmest, with entry, halls and Ut. Rm. in between... within comfort tolerance. (All of Ut. Rm. on return half of loop).

_ 6100 ft. elevation... water boils at 201 - 202 degrees F.

_ We are on a well and septic system... have simple water-test results.

_ We are on a smaller rural electric service... get some outages and bumps... and our house is on the edge of "Lightning Alley". The designer wanted surge protector... "Call 'Brick Wall' and they will figure what is needed". 1 - dedicated 20A circuit was specified for "all". Part of this is 2 plug-ins for zone circulators. Maybe plug-ins for boiler and DHW pump also?... or switches for one or the other of the second two? I don't know about the 'maybe', 'and', 'or' part... they were 'undetermined'... so need advice in this.

*** On the "Control and Wiring Diagram" side there is what looks to be a set up for WWSD. But I think it may not be that... the designer had mentioned, "If you want WWSD auto-shutdown, there would need to be another relay (or relay card?) in the Taco Circulator Relay". I don't know what or why "it" is... whether this is a displaced piece in design evolution, or ??? We had agreed to do manual WWSD.

* Designer would have system pressure gauge marked at pressure point when cold (initial fill... as cold as possible) and marked at "full hot" also... less pressure on gauge shows water loss... add water.

_ The thermostats are shown as tekmar #512. That is outdated. The updated equivalent is #521.

_ There are two tekmar 079 slab sensors for each zone... averaged at the #521's (they are in floor now). The south zone has one in a mostly sun-struck area and the other is in a non-struck area. The north zone has one sensor in each bedroom (east and west sides).

_ This system does not Have to be inexpensive. Maybe 9+ years ago the designer perceived (probably correctly) we had a need to not buy things "just because". The reality of "the right parts" to make a simple, comfortable, easy-functioning system is the higher good... that hasn't changed. Given that, on this existing system design, we will change as change is needed.

Mike Krall

hot_rod

Are you asking for opinions?

If the boiler is going to be an 85,000, really no need for any 1-1/4” piping. Have you priced copper lately? Even if the LLH is 1-1/4, reduce all the piping to 1”. You are only going to get about 76 K from the boiler, the heat load only needs about 4 gpm, so manifolds could also be 1” trunk size m, 1” to the indirect also.

I think the Lochinvar all come with variable speed circs now, that is why the Grundfos number is different. My 50k Lochinvar came with a VS Grundfos boiler circulator

That boilers has all sorts of adjustability, firing limit, step fire, ramp delay, you can really dial it in if you spend some time learning all the parameters and what they do. Learn how the control works, it could take a season to get it exact. Should be videos at the Lochinvar site on that Knight control. The more you know the better the boiler will perform

Really no need to use a relay board with ODR, the boiler has all the control options that you can handle:)

The indirect manual will show the proper piping direction. The hot boiler water against the coldest tank point will be the best.

One 20A circuit is plenty. Some installers add a quality UPS to protect from surges, dirty power, and get some power outage run time

Mike Krall

'Hot Rod', et.al.

I am asking for opinions... and views of this system... and understandings how this system works with 'not all' it's bits and pieces... and, etc.

'Hot Rod' said: "The hot boiler water against the coldest tank point will be the best."

* Is this like the setup for 'best' plate HX function, i.e., counterflow (cold water moving one way.. hot water moving the other)?

* Is there anything about this design's existing indirect configuration that has good attributes with the other aspects of the design (Like scheduled, possibly shorter term heating periods, or other things I can't imagine)?

Mike Krall

hot_rod

I'm not sure what all the commotion is around the zone circs. A circulator, a zone valve and what looks like a balance valve bypass?? Maybe a constant circulation piping arrangement?

Here is a simple constant circulation option with a 3 way zone valve. Ignore the sep, I'm showing the 3 way piping mainly. The tekmar 152 wire to the 3 way zone valves. The end switch triggers the heat call at the boiler.

I'd use delta P circs if the manifold is zoned, Grundfos Alpha or others.

Mike Krall

hot_rod said:

I'm not sure what all the commotion is around the zone circs. A circulator, a zone valve and what looks like a balance valve bypass?? Maybe a constant circulation piping arrangement?

Yes... two 4-loop constant circulation zones.

As I understand it...

The bypass (3/4" Macon STVL) is flow resistance... to have the constant circ. loop NOT be the path of least resistance when the zone valve is open and wants to be delivering heat.

It took me quite a while digging into how that valve could/should be set. In the end, I asked the designer. It is set by starting at full-open. Under 'call' and heat production the valve is closed little by little to get a temp. match between SWT thermostat downstream of LLH and the thermostat downstream of zone circ. "The needed amount of flow".

I believe the 1 1/4" tube (boiler to LLH to zone 1") facilitates the above. The designer mentioned a number of times not wanting to have the system struggle delivering heat the 30+ feet from LLH to remote zone manifolds.

There is an aspect of that last I've never come clear on... the designer preference for 1 1/4" manifold body. What effect would that (what I think of as a small wide-spot in the road just prior to emitter) have? My guesses are: more equal (or ease of) heat to 4 sequential loop take-offs... a place for the 4 zone loop returns to mix different temps... As said, guesses.

Mike

hot_rod

Your call, designers all have different piping and control logic ideas.
A balance valve is a parasitic device, it sheds away some of the pump head. You are running with the throttle wide open and using the brakes to control speed (flow). Not the most elegant solution in my mind.

An ECM delta P circ would use 1/2 the power and adjust flow rate as zones open and close. Loop by loop balance could happen at the manifold.

Since you have constant circulation an ECM makes a lot of sense for your system. Probably pay for the difference in 5 years or so. Hopefully you shut them down during summer months.

Tube size can be easily calculated, it is not about “feel and struggle” opinions 😉

Oversizing pipe brings along other concerns, low flow velocity for one. You have about a 3.7 gpm flow required at design, you could probably cover that with 3/4 tube runs

Mike Krall

hot_rod said:

I'd use delta P circs if the manifold is zoned, Grundfos Alpha or others.

I don't know what you mean, 'Hot Rod'... which circs? What is 'manifold is zoned'?

Mike

hot_rod

Mike Krall said:

hot_rod said:

I'd use delta P circs if the manifold is zoned, Grundfos Alpha or others.

I don't know what you mean, 'Hot Rod'... which circs? What is 'manifold is zoned'?

Mike



I noticed all the different rooms on the manifold and thought they were zones. I'd still consider an ECM circ for energy conservation and data display. If you did add actuators later on the delta P function would be useful.

Mike Krall

OK... I feel like I'm clear on this now. You are recommending looking at variable pumps for the constant circulation aspect of the two manifold zones... depending on loop flow adjustment need (now or maybe later)?

Generally, we are not looking to have specific areas with separate, specific temps.

The south half (lower manifold on diagram) is all open/connected w/ 4 equal loops (my logic is: one temp.).

The 4-loop north 1/2... 2 x bed rm... bath rm... ut.rm./entry... loops (the zone having difference between loop length) looks as if the loop length in each area (for area sq.ft. and heat-loss) will all fall roughly where each area would logically want to fall in temp... like more heat in bathroom and entry/ut.rm... less in bed rooms. To say, I could easily post the N 1/2 loop lengths w/ each area sq.ft. & heat-loss if that would help... just say.

I have occasionally thought having the ability to change flow/heat on north 1/2 loops might be nice (or needed... but not like we couldn't/wouldn't live with it). Are there 4-loop manifolds (preferably with higher volume... you know... the designer) having ..well designed flow control.. a person can also get with thermometer-purge-valve off- air vent? If yes, would you point some out, please?

Mike

hot_rod

I like ECM circs regardless, the modulation features is just icing on the cake, it is there if you ever need it

In partial to the Caleffi brand of components. I do work there. And we do support HH.

Available from most wholesalers.

Mike Krall

Would you use an ECM on the Indirect DHW as well as both constant circ. zones? Same pump as supplied with Lochinvar Knight 55k or 85k?

Mike

hot_rod

The pump that comes with the boiler is an OEM variable speed version that the boiler operates. Here is the one that came with my Knight 050.

I like any of the basic ECM for any circulator application, even in a fixed speed application. They are DC motors, less prone to sticking, have digital readouts for information and settings, etc.
I've used Grundfos Alphas mainly, but plenty of other brands have good options and prices are reasonable.

Mike Krall

Where is the one that came with your Lochinvar Knight... =]

If your view is I can use this OEM Gundfos pump for the other three (indirect and constant) circs., I feel it would make the pump aspect of "spare parts" easier.

Oh yeah... I can't figure out if the OEM pump is... 1. Actually a UPML 25-104... 2. Has internal flow check. Would you say, please?

Mike

hot_rod

Looks like the 55- 155 uses the same pump. Mine is the 25-104, I assume the same for all small models, it does have the check included. Really no reason to use an expensive pump like this for your zone pumps, you don't need the variable speed function. This pump is probably only available from Lochinvar.

Download the manual on the boiler to learn more about the settings, how the pump is controlled, etc. That pump is just for the boiler, use the Alphas for the other circulators.

https://www.lochinvar.com/lit/100305186_2000558066_Rev H_WHB I&O_(51638).pdf

Mike Krall

Hot Rod said:

If the boiler is going to be an 85,000, really no need for any 1-1/4” piping. Have you priced copper lately? Even if the LLH is 1-1/4, reduce all the piping to 1”. You are only going to get about 76 K from the boiler, the heat load only needs about 4 gpm, so manifolds could also be 1” trunk size m, 1” to the indirect also.

The cost between Lochinvar 055k and 085k is quite small. The turn down minimum for those two is 8.3k and 8.5k... very small difference. The designer seemed to be very focused on making DHW hot quickly... the already mentioned aspects of scheduling times for DHW production, getting it done and getting back to heat-load.

What do you see as the pro's and con's of the two sizes for this use? How would you go with it... and, if you would... why?

Oh... and the Viessmann 120/80 LLH is 2"... designer said to step down directly at LLH.

Mike

hot_rod

It really comes down to how quickly YOU want DHW generation. If you pull the tank down to say 100F, will it need to recover in 20 minutes or 40 minutes? That is really what it comes down to when selecting boiler btu/hr. based on DHW wants or needs.

Keep in mind 40 or 50 gallon gas fired water heater tanks are around 34- 40,000 at 75% efficiency. So even a 55K boiler and indirect will out perform a typical gas fired tank.

I have my 55 connected to this flat plate and can make 1.5 gpm continuously, no storage. Basically a homemade 55K combi It does take a minute from a cold start to start running warm. Since it is my shop, that is not a problems, it's mainly truck washing. A Moen shower valve for shop water H&C.
Notice the Alpha to run the DHW plate HX. The other Alpha runs the radiant with a 3 way zone valve (continuous circulation)

Mike Krall

One thing at a time... I know better than to do otherwise... supposedly.

hot_rod said:

It really comes down to how quickly YOU want DHW generation. If you pull the tank down to say 100F, will it need to recover in 20 minutes or 40 minutes? That is really what it comes down to when selecting boiler btu/hr. based on DHW wants or needs.

We do not and will not use a lot of hot water... we worked with the designer on this.. It seems that points to a Lochinvar 55k, not a Lochinvar 85k. The designer decided 85k not 55k. I don't know where else to take that excepting the already mentioned... wanting to make and deliver hot water fast and do it on a limited schedule so the ODR regulated heating was minimally disturbed. * Edited last few words to correct meaning

The boiler sizing question has caused me to wonder if there are differences between the two relating to other aspects. There is no physical size or piping differences and no ... difference in robustness?... somehow better parts supply or cost do to volume of each size made?... different 'boost' capacity deemed to be advantageous? I'm out of misinformed guesses.

No, actually, there's one more: Is the difference between a 55k and an 85k simply that the top end of an 85k was chopped off... like the fan rpm is not allowed to run-up to 85k worth of air/gas mixture?

Mike Krall

hot_rod

Probably not much difference under the hood. The actual boiler HX may be larger, they have an ASME H stamp indicating size.

As for DHW, I ask the customer what they have had in the past for a water heater. If they had a high recovery 75 gallon, they would not be happy with a 50 gallon 51,000 input.

Here is the sticker showing the HX size of my 55 Knight, 5.92 sq ft.

Mike Krall

WHB085 HX = 8.33 sq.ft. https://lochinvar.com/lit/911306WHB-PS-01.pdf

Well, you sort of asked... for 30+ years we have been hot watering on an ancient electric 20 gal. Turn it on mid to late afternoon and turn if off before sleeping. We'd likely be just fine with a SIT030 but the 1.5 deg/hr. loss is annoying (SIT040 0.9 deg/hr loss).

Will a 55k struggle making 40 gallons hot (like 140 -150 deg) on a 1 or 2 time per day basis... like it would take more time away from maintaining slab than ideal... would then need to jump through hoops to catch up and re-stabilize?

Mike

hot_rod

It rare that anyone pulls their tank down to 55F or whatever your cold water supply is. So 50,000 would recover a tank from 100?to a useable temperature of 120 or so in probably 20 minutes or 

An electric tank is around 15,000 BTU/ hr as a comparison, so you would have 4 times the input from the 55,000 boiler choice

Indirects tend to be better insulated than standard gas or electric tanks, around 2” of foam typically.

The hardest load to cover is filling a large tub that holds 50-60 gallons, in a few minutes time

Keep in mind the boiler starts recovering the tank when it drops 10- 15 degrees

Mike Krall

In the above, I was thinking about the DHW indirect in 'maintenance' mode... but I didn't let you know that... sorry...

Would you tell me what you see as pro or con with these ideas?
** Heating DHW 2 or 3 times per 24 hr. (I see cycles being short and at times in day when either heat loss is less or there is plenty of time to catch up.)
** Stepping up one size (SIT-030 to SIT-040)... heating to 140F - 160F and anti-scald mixing to 115F - 120F.

I know a person can roughly do anything... but do you see any silliness in this? If yes, would you un-silly it, please?
--------------------------------------
Tub is 33 gal max... short-end showers (not every day and not morning)

Mike Krall

hot_rod

As long as there is adequate  DHW available  when you need it I suppose you could timer it

A good indirect doesn’t loose much heat if properly piped. It may only call the boiler twice a day by just letting it run, the timer just adds more complexity IMO.

Mike Krall

What is the 'usual' amount of time it takes a boiler to recharge? (Like a 'normal' shave/shower... 40 gal DHW at 140F.)

What difference would a person see for that recharge with 55k and 85k?

To say... I have read a person should set a time for priority DHW... as a hedge against getting stuck and not returning to the heating load... 30 minutes neighborhood (if I'm remembering well).

Mike

Hot_water_fan

To say... I have read a person should set a time for priority DHW... as a hedge against getting stuck and not returning to the heating load... 30 minutes neighborhood (if I'm remembering well).

I wouldn't worry too much. 40 gallons x 8.34 btu/lb x 80 degrees = 26,688 btu, so about a half hour. Doubtful you'll notice heating impacts.

hot_rod

as @Hot_water_fan showed you above. From 60- 140F. You have about 50,000 btu/hr to work with on the 55 boiler

This gets you close. Tanks stratify as you charge or discharge them, so the entire 40 gallons would probably not need to go through that 80° rise. And incoming water may change across the year. Some areas drops to 34F in winter, into the 60's or warmer in summer. Private wells are probably the most consistent in temperature.

Water temp in Phoenix today 89.65F!

Mike Krall

Hot_water_fan & hot_rod...

Thank you for that... all together it made a good picture for me.
51 degree well water... year around (200').
If I get this, 55k(51k) = 35min. and 85k w/ 79k output would be 22min. of "gets you close". That is 2.4% and 1.5% of a day and, likely, both a max and split up over 24hr.
------------------------------------------------------
I mis-wrote above that 'Hot_water_fan then quoted. I'm glad I did because of the response I got... But... what I wanted to know about was setting a maximum time limit a DHW priority call could run. I've found recommendations for doing it and with a 30min.-ish period. The expressed view being getting stuck in DHW priority would be avoided. Is this valid?

Mike

hot_rod

yes you can adjust yes you can adjust the time the boiler stays on a DHW priority call. I doubt you will run the entire tank down to 51F? Doing what?  So if the tank runs down to maybe 90 F while a washer load and dishwasher runs, it seems 15- 20 minutes of DHW call.

In all the years I have been installing system, I have never seen one stuck on DHW, if everything was sized properly

Keep in mind the DHW load can be larger, much larger than the heat load in well insulated, efficient homes. So knowing and designing to the largest load is prudent design practice.

Defining a customers DHW needs is not always an easy task. The more DHW you can supply, the more they will use.

Hot_water_fan

It’s customizable so try different durations.