Why doesn't AFUE work?

John I recently had

the opportunity to design a system from the ground up. Not something that I typicaly do on a daily basis. It was my sons new home. He had certain things he wanted for his heating system so I had to work with what he gave me. Hey I taught him so now I have to live with what I created.

We used a Weil McLain CGi-7, which has a power venter. It is three Hydro air zones, one radiant zone, a modine heater in the garage (not my idea), and the indirect water heater. The radiant uses a Stadler Viega system with indoor outdoor. We have now run this system this past winter with a maximum boiler temp of 150 degrees (F)all winter long. We have proper mixing valve set up with pri/sec piping as recommended by Weil McLain, by the way I wanted to use a Munchkin or an Ultra but my son is apprehensive about new stuff. The DOE on this package is 82.1% AFUE. This boiler has a net I-B-R rating of 144,000 BTU's per hour. This takes into consideration a piping and pickup factor of 1.15. I actually made an allowance due to size of the system that was a little more than 1.15. The DOE heating capacity of this boiler is 166,000 BTU's based on standard DOE tests. The heat loss was done by the engineering department of FW Webb who sold him the boiler. The big user is actually the indirect an WM Gold Plus 80DW. The unit has a power venter and is vented into a masonry chimney with a liner we used an increase to 5" at the outlet of the power venter per Weil McLain instructions. Using some of my own adjustments such as baffling down the power venter air output while monitoring CO, O2 and Stack Temperature my combustion analyzer showed intitally only 72% eff. With further adjustment and measuring actual gas flow with input from the local utility on BTU content we fired the boiler to its maximum capacity. The final result was 86% efficiency with 70 PPM CO air free in the flue. The important thing with this being a cast iron boiler is to not thermally shock the boiler. With our present mixing valve set up and pri/sec piping pumping away we have maintained a return water temp to the boiler of between 138 to 144 degrees. There is no evidence of any condensing problems and in fact this boiler system has an excellent cycle rate at 50% of heating load of about 3 cycles per hour. I would have loved to use a modulating package on this system as it would have been a great set up. But with what I was given to work with it has worked out great. We used a great technicain from Scotland by the name of Chris Stewart to do all the near boiler piping and he did a great job. All the piping in the boiler room is insulated and we use outdoor air for combustion with a single opening to prevent cold air intake when the system is not running. I plan to run some tests on electric power usage on this system as it is zoned using circulators and that must be added into the overall cost to determine real efficiency of a system. I am convinced that our thermal heat transfer (thermal efficiency) is high based on monitored GPM flow and Temperature monitoring a various points in the sytem. Insulating piping is a big factor especially piping to and from the hydro air units. The hydro air units also have to be set up properly which I found the hydronics guys on the job knew nothing about. Insuring proper temp rise across the units and static duct pressures for proper air movement is critical.

The house by the way uses three Guardian air systems to balance the air in the home and works great with First Company air handlers. The Guardian units are about 80% efficient as air exchange units go so there is not a real big loss or gain (AC cooling) in air temp when bringing in fresh air.

I have not had a chance to do a degree day analysis on the system but my son reports his gas bills have been reasonable. They also cook with gas, two outdoor grills and clothes drying. This home also has a seperate gas powered generator with its own gas line and meter due to the need for higher gas pressures. The house is well insualted and has used open design features for good air flow with no walls to contend with. It does have some very high ceilings in spots but proper ducting and air flow control has taken care of that.

I am also convinced as I believe all of us here on the wall can attest to wanting to see better ways to accomplish efficiency. Instruments that need to be developed that give real world analysis and instant information so adjustments are made much simplier. If for no other reason we need to save energy.

I like to control

the amount of flue gas to reduce the size of the package going up the chimney or vent. That will slow the flow velocity and reduce O2 (excess air) and still stay at a safe level, you need to keep an eye on draft. With radiant and possibility of condensation I like to maintain flue gas temp above 300 degrees. I have found the ideal temperature to be around 350 to 450 which is sometimes tough to get but you have to work at it. You really have to go back on some of these jobs a couple of times to get it right.

I measure BTU out by determining GPM flow, gallons of water (converted to lbs) and temperature. I do not have a lot of sophisticated measuring devices, I wish I did but try to estimate as best I can some times. I could use some of that equipment you "lab rats" have. Ideally for every BTU in you get the same BTU out, rare but we can come close. You need to measure temperature at numerous points in the system and also make sure the system is piped correctly. Most problems with poor heat transfer have nothing to do with the boiler but with poor piping and pump set up. We techs have to work with what we are given sometimes and rely on installers to do the job right and then we fine tune it.

A manufacturer usually tests to meet the standards that are set for their package. Some of us in the field will go outside the standard to see how far we can take it without cicumventing safety. Some equipment allows you a great amount of fine tunig. Some equipment is very restricted as to what you can do in the area of fine tuning. Some by the way cannot be tuned and you simply set to specs and hope for the best. Always check O2, Temperature (flue & Stack JIM) and CO. LEAVE THEM SAFE!!!

I like to control

the amount of flue gas to reduce the size of the package going up the chimney or vent. That will slow the flow velocity and reduce O2 (excess air) and still stay at a safe level, you need to keep an eye on draft. With radiant and possibility of condensation I like to maintain flue gas temp above 300 degrees. I have found the ideal temperature to be around 350 to 450 which is sometimes tough to get but you have to work at it. You really have to go back on some of these jobs a couple of times to get it right.

I measure BTU out by determining GPM flow, gallons of water (converted to lbs) and temperature. I do not have a lot of sophisticated measuring devices, I wish I did but try to estimate as best I can some times. I could use some of that equipment you "lab rats" have. Ideally for every BTU in you get the same BTU out, rare but we can come close. You need to measure temperature at numerous points in the system and also make sure the system is piped correctly. Most problems with poor heat transfer have nothing to do with the boiler but with poor piping and pump set up. We techs have to work with what we are given sometimes and rely on installers to do the job right and then we fine tune it.

A manufacturer usually tests to meet the standards that are set for their package. Some of us in the field will go outside the standard to see how far we can take it without cicumventing safety. Some equipment allows you a great amount of fine tunig. Some equipment is very restricted as to what you can do in the area of fine tuning. Some by the way cannot be tuned and you simply set to specs and hope for the best. Always check O2, Temperature (flue & Stack JIM) and CO. LEAVE THEM SAFE!!!

I like to control

the amount of flue gas to reduce the size of the package going up the chimney or vent. That will slow the flow velocity and reduce O2 (excess air) and still stay at a safe level, you need to keep an eye on draft. With radiant and possibility of condensation I like to maintain flue gas temp above 300 degrees. I have found the ideal temperature to be around 350 to 450 which is sometimes tough to get but you have to work at it. You really have to go back on some of these jobs a couple of times to get it right.

I measure BTU out by determining GPM flow, gallons of water (converted to lbs) and temperature. I do not have a lot of sophisticated measuring devices, I wish I did but try to estimate as best I can some times. I could use some of that equipment you "lab rats" have. Ideally for every BTU in you get the same BTU out, rare but we can come close. You need to measure temperature at numerous points in the system and also make sure the system is piped correctly. Most problems with poor heat transfer have nothing to do with the boiler but with poor piping and pump set up. We techs have to work with what we are given sometimes and rely on installers to do the job right and then we fine tune it.

A manufacturer usually tests to meet the standards that are set for their package. Some of us in the field will go outside the standard to see how far we can take it without cicumventing safety. Some equipment allows you a great amount of fine tunig. Some equipment is very restricted as to what you can do in the area of fine tuning. Some by the way cannot be tuned and you simply set to specs and hope for the best. Always check O2, Temperature (flue & Stack JIM) and CO. LEAVE THEM SAFE!!!