Boiler size or problems

Xc8p2dC_2

I purchased a new 3 bed 2bth 1300sq ft home last winter., with Nat Gas FHW 2 zone baseboard.
I noticed a had short cycle boiler issues, the [builder, now defunct] installer came out and looked at it and said it is working normal [but said to set the t stats 5 deg different of each other [yeah right]

If you force test the system by turning the t-stats up and down it cuts in and out OK, the problem is when the tstats is set to a given temp [ie 68 or 70] overnite
The system will fire and will sometimes run for a 15 to 30 secs and someimes a couple of mins every 7-20 mins all night long even at 40deg outside
I have lots of oil burner exp, but new to natgas

The system is a Peerless DE-05 > 140,000 BTU in and 115,000 out
Some I have spoke to said this was to big of a boiler for our size house
and therefore heating the water to quickly
I did a HeatLoss calc and came up around 26,000
Sound possible??????

The other thing that strikes me kinda odd, is when you turn the thermastat up, it takes 1.5+ mins before it opens the zone valves
They do energize @24V as soon as the them is turned up
Is this normal????

What seems to be happening is, the boiler gets up to temp and shuts down, then the next time the zone valves open it circulates the water without having the boiler refire, then as the boiler reaches min temp and starts, it will run for a few seconds, then the t-stats reach room temp and shut it down

Am I more likely to have a boiler size issue or a mechanical problem
TIA for your input

Xc8p2dC_2

Boiler size or probs

Forgot to mention
t-stats are basic Honeywell, mercury
HVAC co set the delay's at .9 for the TACO 007.7 Zvalves

Constantin

Depending where you live,

that boiler indeed sounds way oversized. As a rule of thumb, new homes ought not to loose more than 25BTU/(ft² x hr) in most areas of the US on a design day (there are exceptions, like greenhouses in Alaska).

Knowing nothing more than the information you've given me, I'd say that the heat loss is in the right ballpark and that the boiler is ridiculously oversized (88BTU/(ft² x hr)!!!!). I'd ask the builder to put in the right boiler.

If that's not possible, I'd either yank the system and install a proper boiler or retrofit a buffer tank to reduce the short cycling you're experiencing.

Xc8p2dC_2

Boiler temps

Thanks for the quick reply
Was thinkin a reserve tank as well, but would still be firing at 140K btu for every burn, killin my gas bill
So new unit may be the better choice

I did notice the Tech turned up the high cutoff to around 220 deg and low about 185
What should it be, appox?

jeff_51

tell us where you live

In my neck of the woods, your heat loss would be about 50,000btu. Unless you are in Alaska or something else like heating a green house, sounds like you are way oversized. By the way, my neck of the woods is Minnesota and we do get a bit nippy up here.

Xc8p2dC_2

Boiler size

Live in Eastern Mass >mild winters
I also noticed that the circulator is on the return side about a foot from the boiler, can't win

Tim_24

25 btuh/SF..

is about a bad a rule of thumb as I have ever heard. Constantine, you need to get a better computer program to similate heating your experience. A "standard constructed" home could not be heated in most of the midwest at 25 BTH/SF. Maybe 35 BTUH/SF, but hey you're only 30% off. The best "rule of thumb" is don't use them. If you have to use a ROT, at least be conservative. Yours is not. Plainly bad advice. Experienced gained by running software on your PC, as you have demonstrated very clearly, is not a substitute for actual knowledge and experience.

Constantin

Tim,

You're absolutely right. Rules of thumb ought not to be used for heating systems, hence my advocacy of heat loss programs. After all, the system, emitters, etc. ought to be optimized for each room, and only a heat loss calculation will give you that kind of resolution.

I also qualified my statement about heat loss as "ought to". Clearly, some homes are insulated better than others and some climates are harsher than others. Our home is slated to lose 12BTU/(sq ft. x hr) at -10°F, so 25 BTU/(sq ft. x hr) would be 100% more than what is needed.

In this case, the homeowner calculated a heat loss of about 20BTU/(sq ft x hr) on a design day which seems reasonable. The installer put in a boiler that is 4x oversized for the load. I wonder what conservative rule of thumb that professional used.

Speaking of heat loss programs, I'd like to know what you use, considering that you didn't seem to care for Manual-J-based solutions. Cheers!

Tim_24

The Manual manual

I calculate basic heat loss and gain primarilty using manual methods; pencil, paper and HP32S.

In northern Illinois and Wisconsin, heating design is typically based on -10 degF OAT or more conservatively -15 degF. In the mild New England States (ME excepted), +10 might suffice. However, having seen a lot of new construction in "cost competitive" (i.e. as cheap as code allows) developments, I would be nervous about specifying heat systems at less than 40 BTUH/SF. In my home, I get by with 19 btu/sf. My construction is not avereage by any means.

I once looked over all of the calculated loads I had on hand at the time and saw the numbers range from 10 to 50 btu/sf. For a basic 2x4 contrcted home, w/ r-13 in the wall, r- 35 above ceilings, insulated windows, 35 btu/sf was a solid average.

Again, to say that "most homes in this country" will lose less than 25 btu/sf is inaccurate.

You posted some R values for brick and plaster wall on another thread that was similarly lacking in accuracy. You provided the value for 4" face brick, which is not how brick walls are constructed. I suppose that the website or program you got this information from didn't point that out. The value given for the air space was wrong as well. All in all, incomplete and bad information. Herein lies the difference between really knowing how to determine heat loads vs being able to find some info on the internet or run some sofware that does it all for you. I used to fume at the old guy that taught me to do these things manually because of the prevalence of computer softwares that would do it for me. Now, thanks to posts like yours, I fully realize the value of that education that no software can approach.
Cheers

Constantin

Thanks for the feedback Tim,

I'll take your advice and change the upper end of my ballpark for "normal" heat losses to 35BTU/(ft² x hr). Many installers here have stated that they use 25BTU's as a ballpark starting point, and I made the mistake of following their lead. Obviously, construction standards vary, some installers here may only see the better structures that can get built and besides, the climate also varies a great deal.

I'm also happy for you that the manual approach you've come to appreciate works as well as it does for you. How do the numbers compare between Manual-J, 7th or 8th Ed. vs. your results? In what are the areas do they diverge significantly?

Another question that your method brings up is speed. Even with the help of your calculator, how long does each home take you to calculate? Do you just work on large developments where hundreds of similar homes are being built, or on-off homes as well?

As for the Colorado web-site, why don't you contact them and educate them about the error of their ways directly. Otherwise, more consumers and professionals may be led down (what is in your opinon) a stray path. I assumed a single-brick-thick wall since the OP noted nothing thicker, perhaps there are more layers. Lastly, your observations regarding that wall may perhaps be of better value in the relevant thread than in this one.

Dick Charland

Give me a call

I work for E.R. Stephen Co., we are the Peerless rep. I will be glad to stop by and check out what is going on. Though the boiler does sound over sized, the short cycling problem sounds like something else. You can reach me at (800) 649-6789 or via my e-mail. Be glad to help get it straightened out.

Tim_24

Comparisons...

between this manual method and commecial softwares have been made in the past, though not specifcally with the ACCA products. Carrier and Trane had commercial load calulating software that compared within expected margins of error, which BTW are on the order, for ALL h/c load calculations for occupied buildings, of 15%. Divergences, when all assumptions were chased down and rectified, were negligible. Different values have been estimated by different folks over the years. As far as speed goes, you are absolutely correct. Time is money. However, large subdevelopers, usually don't bother with engineers or use a few select models. Custom homes are a different matter. I can knock out a 12 room house, doing room by room loads, in a few (3 or so) hours, by hand. Again, very few homeowners or builders will pay for engineering. Not a great portion of my business.

My point about the wall is that the data you posted was correct, for instance, I use 0.44 for 4" face brick and 0.17 for and outside air surface (with 15 mph assumed wind speed) and 0.68 for the inside air surface (vertical sufaces only), however, the information was not. For an air gap I use 0.85, minor difference and you forgot the plaster surface, typically 3/4 - 1" thick with lathing inside, composite R value of about 0.7. The (structural) brick wall would be a minimum of 12" thick, which would triple the R-value of the brick. There is nothing in the OP that says so, nor is there anything in the tabulated data on the thermal properties of building materials that says so. Anyone who has calculated heating and cooling loads in an old masonry building, the only type you would expect a brick and plaster wall to be used, would know that or have a good base of knowledge to make such an engineering judgement. The website provided you with accurate information, however it was not interpreted correctly or completely. Not necessarily picking on you, just pointing out that your well researched data requires some experience and prespective to become useful information. My overall R value for that wall would have been 3.7 vs your 2.3, a 38% difference.

Regardless of our methods and experiences, giving unseasoned folks square foot numbers is, IMHO, illadvised.

jerry scharf_3

answering parts of your post

I agree with ****, the boiler may be oversized but that should not cause short cycling as described.

It sounds like you have some serious control system problems. Zone valves can take up to 120s to open, depending on the type installed. There are usually limit switches on the valve that you use to delay the rest of the control operation till the valve is fully open. Even that doesn't explain all of what you describe.

It really sucks that the builder packed up and stuck you with the mess. Sadly, my guess is you are going to have to pay for someone to fix the mess. Take **** up on his kind offer to come out and see what he thinks needs to be done.

best of luck,

jerry

Bob W._3

Tim, that is interesting info on the brick wall. There are a lot of variations in construction. I would not assume plaster over lath, for instance. Our walls are 3 wythe, 1&1/2" air space, plaster applied directly on the inner course. I have seen 2 wythe, no air space, plaster over lath. My question is how is the thermal mass figured in? Data suggests that the large thermal mass makes the wall perform better than the "R" value, which would, of course, affect the heat loss calculation. Where do we go for this data?

Tim_24

Thermal mass...

has more to do with the response of the structure to transients than it has to do with steady state load calculations. There is an evolving body of evidence to suggest that such simplistic methods may be inadequate in completely defining the effect of the thermal mass on the R value, yet it is still evolving. I am keeping up with these developements. I have yet to see definitive evidence that the actual R value is modified by the presence of greater mass. In commercial computations, especially when time-of-day energy anaylsis is required for design a Thermal Energy Storage system, the buidling is characterized by the mass and responses to thermal transients can be determined. This type of computation is not well suited to manual methods, and I don't do them by hand.

Assuming certain features of the wall structure were actually based on an old masonry structure that I analyzed once upon a time. I worked up a composite of the lath and plaster wall structure from a sample that was exposed during a renovation. I used a gypsum/fiber concrete data to approximate the horse hair laden plaster that I measure to be an 1" in places, and assumed 1-1/2" wide x 1/4" thick lathing with 1/4" gaps. The "concrete" alone was good for 0.6 R/in. In actual jobs, I verify building structural details by inspection.

As to where do we go for this data, the basic thermal properties of building materials is available from many sources, ASHRAE Fundamentals Handbook being my favorite, but building science websites and manufacturers' published data are other sources. As far as the effects on thermal resistence due to mass there are several studies done and or inprogress, though I don't have details handy. As far as wall construction details, eyeball reference is surpassed by none. Go out and look at building details. Attics and basements, crawlspaces too, are the best places in existing structures. In most old buildings I have worked, I usually found the top of a wall accessible somewhere. You can mind getting dirty though. Look at construction sites if you can. I love looking at construction in progress. The details are there to be examined.

Xc8p2dC_2

Boiler size

Thanks ****
I will follow up by phone
and thanks to all other that posted, lots of great info in this site
Rick Alan

Bob W._3

I'm still trying to figure out if our home, which is one big thermal bridge, is still "relatively" efficient because of the large thermal mass (the aforementioned outer walls, plus three floors of poured concrete and thick weight bearing brick inner walls to support the same). The heat bills are fairly high, but part of that is due to the fact that we are heating essentially four floors (since the basement is quite warm) and using a single pipe steam system. Even assuming we are heating only three floors (+/- 4500 sq. ft., adjusted for ceiling heights) our energy usage is just under 15BTU/Sq.Ft./HDD, which is about average for an old (1910)house. That is without wall insulation. Mass must count for something but it is hard to quantify.

Tim_24

Wearing the designer hat,

my first responsibility is to determine the necessary capacity of the equipment to be selected to meet the design conditions and occupancy of the space. In that process, relative thermal efficiency of the structure is immaterial. As long as the details of construction are known, wether they be poor or exceptional, the necessary equipment capacity can be determined. If a detail, such as the R value of a lath and plaster wall coating, has to be estimated, the designer knows, or hopefully knows, the conservatism or lack of, that is contained in their assumptions. As to how the systems and the structure respond to changing conditions and partial load operation, that is a controls issue. This would be addressed as the design progresses into greater detail.

Information like BTUH/SF/HDD is not useful in determining peak loads or selecting equipment capacities. It is important in evaluating options and potential upgrades.