Heat Loss per Hour?

Martin Romero

So if my heatloss according to the Slant Fin software is 26,000 BTU/Hr or so, then do I need enough panels to produce a certain percentage of that load at the same design temperature?

Thanks for your help,

Mart

Martin Romero

Heat Loss per Hour?

I used the Slant Fin Heat Loss Calculation tool and found my heat loss to be 26,558 BTU/Hr. Is this per degree day, or what is the baseline measure?

Ron Gillen

At Design

This is the BTU/H your system is required to produce at design or on the coldest day expected for your area.

Robert O'Brien

Surprising?

Isn't it? Just out of curiosity what size boiler do you currently have?

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Martin Romero

Design Temp and Boiler size

Thanks for your responses.

I have only a vague understanding of design temperature. Can you clarify a bit? My boiler is rated at 64,000 BTU/hr.

I hope to use this information to help size a solar support system for my radiant floor heating.


grateful,

Mart

jp_2

design temperature

is any outside temperature you want to use to determine the temperature difference between inside and outside. then you can determine heatloss or heatload needed.

general you use the coldest expected temperature for your area. but you may also be curious what goes on when its 43F outside too.

Mike T., Swampeast MO

Heat loss calculations produce a reasonable estimate of the maximum heat load that the system will see. In most places, this maximum heat load is required only a very tiny amount of time, if ever.

While the heat loss calculation provides a reasonable design load (your emitters must be capable of liberating that much energy), it takes more than heat loss alone to size the emitters.

To properly size emitters, you must consider the average temperature at which they will operate. Solar systems are generally considered "low temperature" heat sources. This doesn't mean that they can't produce high temperatures, but as the temp difference between the fluid temp its producing and the air surrounding the collector increases, efficiency decreases. When you consider that the least solar energy is available when you need it most (winter), this virtually requires that a solar space heating system be able to supply the required energy at a fairly low temperature. The efficiency of evacuated tube collectors does not drop nearly as fast as with conventional flat panels, but it drops nonetheless.

IMHO, the best solar space heating systems have very good passive solar gain characteristics. This means that most of the energy collected during peak times can go to storage instead of heating the structure. A well designed "sun room" with a very high mass (thick concrete/stone/brick/etc.), insulated floor can itself act as a thermal battery that will give off its' heat slowly and gently for a long time after the sun stops shining. Deep eaves (selected for your latitude) are an absolute must but even then overheating is a near guarantee in some conditions. For that reason some sort of movable window covering (automatic is by far best) should be included in the design.

jp_2

slight correction

"""To properly size emitters, you must consider the average temperature at which they will operate.""""

you want to size the emitters for the highest temperature you plan to use. if you use average temp, you will greatly oversize the emitters. as in panel rads or similar, size is money and oversizing is waste that good old money, money could be spend on big screen TV, add the heatload of that too.

Unknown

I think he means average temp across the emitter (supply to return) which allows for funky fun with flow rates.

jp_2

why?

whats the difference between talking about temp difference or needed btu's? they are basically equivalent.

I have not really seen any solar collectors rated in delta T?
normally just btu's.

Unknown

you can't talk about supply temp requirements to the emitter without noting the flow rate, or the number is meaningless.

You can, however, talk about average temps across an emitter (like a radiant floor) and it's universal; doesn't matter if you do average +5 at a ten degree drop or average +10 at a twenty degree drop, the average temp is the same. and average temp in an emitter is what determines overall output from the emitter.

Solar collectors are not emitters.

jp_2

????????????

who said a collector is an emitter? is a inny an outy?

I guess I do not know what you are refering to here at all?

not what i was talking about?

Unknown

You were saying if he sized for average temp he'd "oversize" his emitters. That was not correct. Then you started talking about solar collectors, seemingly out of the blue.

If I'm missing something, so be it.