Lochinvar Space Heat Limiting.

Peregrine

This is a Lochinvar Noble Combi 150NKC N natural gas 150k BTUH. The combi is 3X oversized and a heat loss calculation is 48k BTUH; it is a 1250 sq foot unit so that number might be in line.

The space heat set point coldest day is 125, outdoor temp coldest day is 15, max space heat set point is 150 and design day temp is negative 7.That negative 7 degree number is gotten from the ASHRAE ODT Conversion factor table; the house it at 8000 feet and Leadville is 10,000 feet and that number is negative 14 degrees. House temp is set to 68 degrees in the bedrooms and 70 degrees in the living room.

The max space heat limiting is set to 10% and I know that is too low and not to normal standards. But the average cycle time defined as start to off to start again is 1X per hour or 60 minutes and significantly over an hour when it gets under 15 degrees (coldest day set point). The house temp is at TSAT set points and the combi does meet specifications to shut off at 8 degrees over space heat max when 10 degrees outside and runs runs and runs when it gets under 5 degrees. The house is always warm.

I am sure space heat limiting will have to be raised for the same performance when it gets to design day temps of negative 7.

The therm use is up an estimated 3% over what is normal but it runs and runs and runs. The choice has been made to sacrifice the extra therms for a longer cycle time.

I realize a response is going to be that the heat calculation is wrong.

Feedback please on impacts to control board, gas valve, blower and pump.

Thanks and have a Great day.

hot_rod

I know the Lochinvar Knight has a boost function that will overide the ODR, and I think the SH limit, if the boiler is not maintaining. Look in the manual to see if this is available on the Nobel. It is a useful parameter.

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Peregrine

its working perfect, I think, is what Im saying. I set it to 10%. it is condensing condensing condensing; running running running. i was looking for feedback if i am damaging any components ie. heat exchanger, control board, gas valve or blower or anything else.

have a Geat day

Thanks

LRCCBJ

The requirement of 48K at design is completely wrong for two reasons:

1. You'd need to leave all the windows open to lose 38 BTU/sq.ft
2. ]Your own data with the SH at 10% confirms that the space maintains temperature at 15K…………maybe a bit more at design. I'd be very surprised if you had to raise the 10% to 20%. The boiler is much too large for the space.

No, you are not damaging anything. The boiler is perfectly happy to run at low modulation levels……………forever. But, you cannot get forever because the boiler is too large and it cycles. A boiler one-half that size can run for six months consistently with no shutdown for a house that is 2X that size with a design temp of 6F.

……………the downside of combis……………..

GroundUp

Assuming this is a radiant floor system, you need to adjust the water temp rather than the SH limit. Turn the coldest day setpoint down to 95* and it'll limit the heating by itself, while simultaneously keeping the heat exchanger happier than being at low fire for its entire life.