Alpine Boiler question
New to the forum and first post.
Last Fall I had the old VHE boiler removed and a new system with a Burnham Alpine 150 installed.
I have come to realize my plumber has no idea on how to set up this new type of boiler.
When the cold weather hit we could not keep the house warm. His suggestion was to install additional heat under the sink area in the kitchen. I told him that we never had a heat problem with the old system and this boiler you recommended has a higher BTU rating. Long story, but the short of it is with manual in hand, a stool I spent several hours in the basement monitoering the operation. It soon became aparent that it was short cycling and shutting down due to a temp overshoot when it fired up. I reset the factory overshoot of 2deg to 10 and that helped a bunch.
My question now is what effect does the boiler pump speed have on the system? I am bumping of the low limit much/most of the time now that temps are in the upper 30's, and the return D/T is less than 3or4 deg much of the time.
Thanks for any help.
I would find a qualified heating tech not a plumber to look it over, the fact that they upsized the boiler shows there incompetence, unless it had trouble maintaining before?
Over-sizing will cause the boiler to short cycle and reduce its efficiency and life.
A heat loss calculation should have been done and the boiler sized to that. Zoning should be eliminated or minimized as that also will cause short cycling with a mod/con due to its low mass.
You may have to install a buffer tank to get some mass back in the system and compensate for over-sizing and any zoning. The buffer tank would be sized to cover the difference between the minimum firing rate and the smallest zone demand on the system.
A combustion analysis with a digital analyzer is required on that boiler as well. Your plumber is probably clueless about that too.
Try the contractor locator to find a pro in your area. Ask them if they are competent with mod/con boilers; if the can do a combustion analysis, etc. If not, search for one who can.
Also, was the boiler piped primary/secondary as the manufacturer requires? Was the Grundfos ups26-99 circulator that came with the boiler used on the primary loop?
You're gonna have a very pre-mature boiler failure if you don't get a competent hydronics pro to correct your problems and do yearly maintenance on the Alpine.
You can choose to do what you want, but you cannot choose the consequences.
Sorry, primary/secondary,where the distribution system of the hydronic heating system drive the terminals (radiantion) and the heat transfer from fire to boiler is drive by its own "secondary" pump. Old-fashioned cast iron boilers wasted enough heat up flue, out jacket and collected enough via heavy mass to go without an extra circulator (talking residential).
With low-mass boilers using more noble, lighter weight materials such as steel, copper, aluminum and stainless steel the output to mass ratio makes minimum flow critical as under-pumping will lead to cavitation (makes noise when under fire). This is not an excuse to over-pump however (waste electricity, lift pressure relief valves (PRV) and cause flow noise and erosion.
When designing hydronic systems with low-mass boilers the first order of business is to make sure that now zone in the system--able to call the boiler itself--is capable of unloading the boiler at minimum fire and providing the minimum flow required at that out put.
It is easier to use P/S for everything, like wearing you pulling a trailer behind your truck. But it doesn't make it right. When converting an old gravity boiler connected to cast iron radiators with 3" black pipe, one zone, essentially no pressure drop in the distribution piping. One condensing boiler, one pump sized to the boiler load, program outdoor reset, save the customer 50% on the fuel bill, and $500.00 on the pump he didn't need.
Don't try this with Buderus, Weil McLain or SlantFin as the have taken the P/S pill CYA with the customer's money.
More progressive manufacturers, Burnham, Bosch, ICB, NTI and Viessmann for example, will let a thinking man do the math and build the system that best fits the job.
Most of the ModCons we service are too big and could have been improved with better near-piping, some with P/S and some most certainly without.
Alpine, Bosch, Buderus, Ultra, Prestige, Contender, Vitodens...it is all about the contractor. They should hold at least one factory certification for condensing boilers. Some plumbers are smarter than others...
I wonder if the old boiler had it's own circulator and the primary loop had a higher flow rate. The circulator for wall mount boielr are usually designed for 30 or even 50F delta T from supply to return water at max fire. Some COMBI boilers need a 70F delta T, meaning in reality, you will rarely reach max fire during space heating, only with cold domestic supply water.
That being said, sometimes condensing boielr don't work well on retrofits if you don't have enough radiation for utilizing supply temps of 160F or lower. Remember a condensing boiler's effceincy is all abotu return water temp. It's ONLY a 90%+ boiler when return water is <120F, otherwise it's no better than a 86% cast iron boiler. Return water is actually limited to 160F so you don't melt the PVC pipe since there's a direct correlation of flue gas temps and effciency. That wasted heat of course has to go somewhere. Return temps over 160 require a SS flue.
You hired a plumber. Thats a first mistake.
Hey now, I am a plumber--but have to admit, I started in tin.
It is true that some ModCons will not fire above 167°F e.g. Viessmann Vitodens (makes more sense in at the equivalent 75°C) but it is fairly rare that an existing fin-tube radiated home will need to run at maximum potential output say 190 in and 170°F back at 4gpm. But it obviously pays to measure.
Most ModCons can be run to 190° and will for the production of DHW. But for this incidental load and perhaps for the rare system with minimum fin-tube baseboard during the coldest 5 days of the year, most condensing boiler when properly sized, piped and programmed will not need to operate at 180°F average water temperature.
With the right reset curve programmed for fin-tube baseboard and the right-sized boiler, most of the heating season will be served with 110°F-160°F supply water, putting the return (at a typical 20° delta T) firmly in the condensing zone.
Most ModCon manufacturers are happy with a 20-35° delta T (none of the 16 manufactures we have used will tolerate anywhere near a 70°F delta T but if you measure on and the unit is still firing it could be a clue since the burner will have modulated to an output far below its potential) but this has little to do with the typical baseboard system operating at a 20°F delta T at 1 gpm, unless you have engineered the system with one pump. No, not all ModCons must be piped P/S, but some manufacturers do tie warranty to this seemly idiot-proof piping strategy. Buderus, Weil McLain and Slant Fin would be in this small group.
No ModCon that we have installed operates below 86% combustion efficiency regardless of the operation water temperature.
Obviously the key to success when specifying, installing or commissioning and hydronic heating system is reading and understanding the installation manual and properly applying the information found therein.
WHen a mod con runs at 190F for domestic water, I suspect the return water comming back frmo the P&F HE is <160F. With exception to low fire or low flow situations. At low fire, the HE is ovesized, so depite high return water temps, the flue gas temps stay low.
That is anothe point, because there's a HE involved, a combi isn't quite as effcient as a regular tankless in low flow conditions, because it always runs high supply temps without the belefit of low retun temps. WHereas in a tankless, the retrun temps are equal to the incomming domestic water temps, so usually <70F. IN mid winter when you are really pushing max capacity it might be 35F in a cold climate. I have to admit grinning a little visualizing my tankless blasting away at max fire while I filled a soaking tub this weekend. It would have completely drained our old 40 gallon tank and taken about an hour to recover.
Thank you all again for the excellent replies.
I have contacted a large well respected HVAC company in my area ssed that the gal answering the phone knew absolutely what a Manual J was and said they do one for every new or retrofit installation. They are sending their senior tech who is Alpine trained she said over next week to do the study.
I would like to mention here for everyone that might have been in my shoes when deciding on a new system. I did have 3 estimates. The company comming over next week was one of them. They were the highest of the bids. In retrospect they would have been the smartest choice. I did not do my research before deciding on a plumber.
I am still confused about the con side of these boilers. At a delta t of 20deg the max the output temp could be is around 140 to stay in the condencing mode as I read it. I only see, after a zone is on and run for a minute or so as to get the hot water through the loop, a temp difference of maybe 6-10 deg. I assume this is due to not enough thermal mass to extract more heat. It is I guess,also somewhat infulenced by the flow rate of the zone. There are ball valves on both sides of each zone pump but were all left wide open. Yes, it was plumbed with a primary and secondary loop using the Grundfos ups26-99 pump. The pump was set to the highest speed by the plumber. According to the manual the pump is supposed to be set to the "First Speed". I reset it to the lowest speed. Will that have much effect on the delta t?
Again, that you all for the excellent help and advice.
No Free Lunch
I wish that everyone who is planning on a boiler or HVAC replacement would read and heed these words. Customers need to look for the best value, not the cheapest price. To get the best value almost always involves spending more money up front to save $$$ in the long run. The man with the higher bid probably has more included in his bid - particularly knowledge and experience.
Originally Posted by tom3holer
Also, because someone is a "plumber" or "HVAC Tech" doesn't mean they know anything about hydronics, especially mod/cons.
Regarding your system Delta T: most will not approach the 20* design unless it's near design temp outside (0-10*). A 6-10* Delta T on the system is not unusual, though not "ideal". Unless you can reduce the zone's circulator speed, I wouldn't worry about it. This is why variable speed Delta T and Delta P pumps are becoming more popular. They not only reduce energy consumption, but you can fine tune the system with them.
Originally Posted by tom3holer
Lowering the speed on the boiler pump will widen the delta T on it, but not necessarily the system.
Make sure the outdoor sensor is installed and the reset curve is properly set to match the load and system design; that will do far more to keep the boiler condensing and saving energy than anything else you could do.
You can choose to do what you want, but you cannot choose the consequences.
There may be two delta Ts. If piped P/S the low-mass boiler will typically require a minimum flow between 20 and 35 degrees but the system delta T is based on the radiation. The "con" will begin when the return temperature to the "boiler" approaches 130°F.
In residential HVAC work it is a good idea to through the low bid out and try to distinguish between those that are left, the one with a sample Manual 'J' getting extra credit.
I unfortunate how this relatively simple premise is misunderstood by those that install boilers. Virtually every mod-con boiler installation manual shows a P/S system as a requirement. It's too difficult to maintain the delta T and minimum flow you need for it to run efficeintly without it over a wide range of loads, and is a common reason why many sytems end up load restricted.