Is my heating curve good enough?

pieIX

Here is the description of the heating system.

It is a 1953 building with 4 floors (31 feet up to the top of the last radiator) including the basement with original insulation and thermos windows. There are 6 apartments of 1000 sq. ft. with 8 radiators, two 3 ½ in the basement and a common area. The building is in Montreal (-9F outdoor design).

There are two Buderus condensing boilers one of 160,000 BTU (GB142/45) and one of 200,000 BTU (GB142/60). The 45 is for heating and 60 is for hot water. There are two pumps for each boiler (heating and DHW). The 60 can help the 45 if there is a lack of power (i.e system startup). The LOAD parameter for boiler 45 has been reduced to 95 in order to have a minimum cycle of 15 minutes. There is no "Load balancing" between the two boilers.

The DHW sensors are connected directly to the two boilers and only boiler 60 is used for the DHW during the heating period. According to statistics, the heating of hot water does not influence the heating of the building.

The system is cold started at a pressure of 17 PSI@60F (regulator and 13.2 gallons expansion tank 2 x 6.6 gallons). The pressure can rise to 26 PSI on the gauge at the side of the regulator for an outside temperature of –15F. But the pressure display by the boilers is 29-30 PSI (safety valves at 30psi!!). The maximum boiler supply is at 130F not to bust the safety valves and the boiler design is at 138F (heating curve 0.8).

In several apartments (4/8) there are thermometers to calibrate the system and record statistics and they do not control the boilers.

Here are the parameters of the Tekmar 261 (outdoor reset):
OCC = 58F (but it is 68F inside)
UNOCC = 58F
OUTDOOR DESIGN = -15F
TYPE OF TERMINAL = 5 (radiator)
TARGET SET POINT = OFF
DESIGN INDOOR = 70F
DESIGN SUPPLY = 138F (0,80) formula X=(B-C)/(C-D)
MAXIMUM BOILER SUPPLY = 130F
MINIMUM BOILER SUPPLY = OFF
TIME DELAY = 0:10
DIFFERENTIAL = AUTO
OCC SYSTEM WORM WEATHER SHUT DOWN = 68F
UNOCC SYSTEM WORM WEATHER SHUT DOWN = 68F

The problem is that there is an apartment on the 4th floor with the same size and the same number of radiators (8) which is hotter by 44.6F than the other identical apartment (66F). There are “auto bleeder” on the radiators. So not a bleeding problem. This difference prohibits increasing the temperature of the system (not to cook the tenants of the the 4th floor). There is also another apartment this one in the basement which is also at 78.8F. Its number of radiator is different as well as its size.

The “supply” splits in two at the beginning of the piping circuit. My guess is that the two apartments are at the beginning of these loops and that's why the temperature difference is so big. I believe that the radiators of these apartments in problem should be balanced.

Is it your diagnostic? And is the heating curve good enough for this type of building?

That’s it. Thanks for your help.