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Run time vs right-sizing

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Run time vs right-sizing Vance 12-07-2006
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Posted by Vance on December 7, 2006, 2:39 am
At -10C, which is also my design temp, my condensing gas furnace runs for 20
mins every 2 hours to maintain a setpoint of 18C with a spread of .5C,
obviously it is theoretically oversized, however, if sized 'correctly' it
would run continuously at -10C and use significantly more KWH's. Which would
be the better scenario, almost continuous run times to improve comfort at
the expense of higher electricity usage or the shorter cycles with less wear
on the blower and draft inducer fan?



Posted by Bubba on December 7, 2006, 7:39 am
wrote:

>At -10C, which is also my design temp, my condensing gas furnace runs for 20
>mins every 2 hours to maintain a setpoint of 18C with a spread of .5C,
>obviously it is theoretically oversized, however, if sized 'correctly' it
>would run continuously at -10C and use significantly more KWH's. Which would
>be the better scenario, almost continuous run times to improve comfort at
>the expense of higher electricity usage or the shorter cycles with less wear
>on the blower and draft inducer fan?
>

WRONG! If it were sized correctly, it would have longer run times
using a smaller KW heater. Thus balancing out the electric
consumption. It is always better to properly size a furnace.
Bubba

Posted by Vance on December 7, 2006, 1:50 pm

> wrote:
>
>>At -10C, which is also my design temp, my condensing gas furnace runs for
>>20
>>mins every 2 hours to maintain a setpoint of 18C with a spread of .5C,
>>obviously it is theoretically oversized, however, if sized 'correctly' it
>>would run continuously at -10C and use significantly more KWH's. Which
>>would
>>be the better scenario, almost continuous run times to improve comfort at
>>the expense of higher electricity usage or the shorter cycles with less
>>wear
>>on the blower and draft inducer fan?
>>
>
> WRONG! If it were sized correctly, it would have longer run times
> using a smaller KW heater. Thus balancing out the electric
> consumption. It is always better to properly size a furnace.
> Bubba

There are no heat strips in this application - gas only. A smaller furnace
would cost more to operate and maintain due to much longer run times. 20 min
run times are certainly not short cycling nor reducing the efficiency of the
furnace.



Posted by Bubba on December 7, 2006, 8:01 pm

>
>> wrote:
>>
>>>At -10C, which is also my design temp, my condensing gas furnace runs for
>>>20
>>>mins every 2 hours to maintain a setpoint of 18C with a spread of .5C,
>>>obviously it is theoretically oversized, however, if sized 'correctly' it
>>>would run continuously at -10C and use significantly more KWH's. Which
>>>would
>>>be the better scenario, almost continuous run times to improve comfort at
>>>the expense of higher electricity usage or the shorter cycles with less
>>>wear
>>>on the blower and draft inducer fan?
>>>
>>
>> WRONG! If it were sized correctly, it would have longer run times
>> using a smaller KW heater. Thus balancing out the electric
>> consumption. It is always better to properly size a furnace.
>> Bubba
>
>There are no heat strips in this application - gas only. A smaller furnace
>would cost more to operate and maintain due to much longer run times. 20 min
>run times are certainly not short cycling nor reducing the efficiency of the
>furnace.
>
Interesting how you "use significantly more KWH's" as you point out.
KWH's would be Kilo-Watt-hours. Those would be electric numbers
junior.
A smaller furnace would NOT cost more to operated and maintain.
20 min run times per 2 HOURS at design temperature IS definately
over-sized.
You're an IDIOT and/or TROLL.
Bubba

Posted by Vance on December 7, 2006, 10:38 pm

>
>>
>>> wrote:
>>>
>>>>At -10C, which is also my design temp, my condensing gas furnace runs
>>>>for
>>>>20
>>>>mins every 2 hours to maintain a setpoint of 18C with a spread of .5C,
>>>>obviously it is theoretically oversized, however, if sized 'correctly'
>>>>it
>>>>would run continuously at -10C and use significantly more KWH's. Which
>>>>would
>>>>be the better scenario, almost continuous run times to improve comfort
>>>>at
>>>>the expense of higher electricity usage or the shorter cycles with less
>>>>wear
>>>>on the blower and draft inducer fan?
>>>>
>>>
>>> WRONG! If it were sized correctly, it would have longer run times
>>> using a smaller KW heater. Thus balancing out the electric
>>> consumption. It is always better to properly size a furnace.
>>> Bubba
>>
>>There are no heat strips in this application - gas only. A smaller furnace
>>would cost more to operate and maintain due to much longer run times. 20
>>min
>>run times are certainly not short cycling nor reducing the efficiency of
>>the
>>furnace.
>>
> Interesting how you "use significantly more KWH's" as you point out.
> KWH's would be Kilo-Watt-hours. Those would be electric numbers
> junior.
> A smaller furnace would NOT cost more to operated and maintain.
> 20 min run times per 2 HOURS at design temperature IS definately
> over-sized.
> You're an IDIOT and/or TROLL.


You are either uneducated, misinformed or both.

Let me expand on "Those would be electric numbers":

KWH is a standard symbol representing power usage usually in the form kWh
which is 1000 watts used for a period of 1 hour. If the smaller furnace has
a 1/2 HP motor drawing 4A it will consume 1452 kWh in a 6 month heating
season (4*120*24*30*6*.7/1000) with a 70% duty cycle whereas the larger
furnace will consume only 207 kWh with a 10% duty cycle. At 20cents/kWh the
difference will heat my home for 4 months. This does not even take into
consideration the inducer fan or increased wear and maintenance costs.



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