BTU NEEDS

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I have a new sun porch that is 36'X8'X8.5'. It is super insulated with a double layer all around of R19 and a foam underlayment of R11. One side of the sun room are six large windows and a glass door.

How do I compute the BTU load so I can hook up a proper length of cast iron baseboard radiator. (I dont have it as a separate zone so if I make the radiator too long, itll turn the room to a sauna) SO, Ive got the approx BTU values per ft of radiator. Now what do I do for the room. PS it faces EAst.

I can just oversize the baseboards but dont want to

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Priming the pump.

Bump.

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Well, how much sunlight do you receive, and which way to the windows face?

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faces east, get wintertime sun about from 7:30 AM till about 2PM. The windows are high E but since theres so much glass on that side , it loses the thermal mass effect real quickly after sunpassage.. If I had a trombe wall behind , itd be more heat mass but Id lose some floor space. Its only 8.5 ft wide.

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Re: BTU NEEDS

farmerman wrote:

I have a new sun porch that is 36'X8'X8.5'. It is super insulated with a double layer all around of R19 and a foam underlayment of R11. One side of the sun room are six large windows and a glass door.

How do I compute the BTU load so I can hook up a proper length of cast iron baseboard radiator. (I dont have it as a separate zone so if I make the radiator too long, itll turn the room to a sauna) SO, Ive got the approx BTU values per ft of radiator. Now what do I do for the room. PS it faces EAst.

I can just oversize the baseboards but dont want to

First, FM, you need to find out your Outdoor Winter Design Temperature for your city.

http://www.engineeringtoolbox.com/us-outdoor-design-temperature-humidity-d_296.html

Then, Indoor temperature minus OWDT = Delta T [Is there a delta sign on a computer keyboard?]

1. Square foot of insulated wall x U value [the reciprocal of the R factor; R20 = 0.05 U-value] x Delta T = Hourly heat loss for this part of the wall system

EXAMPLE: Columbus, Ohio minus 10; Indoor design temp 70 degrees = Delta T of 80 degrees

Area of wall - 36 x 8.5 = 306sf - [any windows; assume none]

Heat loss = 306sf x .0263 [u-value for R38] x 80 [Delta T] = 643.8 BTUs per hour

2. Repeat for any other wall components, windows, glass door, floor and ceiling.

3. Depending on how air tight you've made it, you'll have to add anywhere from 1/2 an air change per hour down to whatever. You can determine this with an air blower test but to my mind it's not worth it.

Since a heat loss is done for the coldest day one should encounter, the heating system should be fine for all the other days. I'd just go with 1/2 the volume of the room as the hourly air change.

I've forgotten how the air infiltration loss is calculated. Let me rack my brain a bit [or should I waterboard it as this seems to be in vogue] or do some checking.

You should/could add in the solar gain from the east facing windows, though for the OWDT day, it probably won't make a great deal of difference.

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Thanks. I can follow that, pretty st fwd. OT-IT =(delta). Then use COldest day of the year concept and hest loss/hr. Got it.
. Im gonna run a sample calc then take it to my contractor for conversion to baseboard cast iron needs.

My problem is that I dont wanna run a separate zone here and Im only going to put in a slave bypass kind of switch ( radiator section ), and this will either be "on" or "Off"). That area of the house is on a separate zone for the room from which the porch extends.

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farmerman wrote:

Thanks. I can follow that, pretty st fwd. OT-IT =(delta). Then use COldest day of the year concept and hest loss/hr. Got it.
. Im gonna run a sample calc then take it to my contractor for conversion to baseboard cast iron needs.

My problem is that I dont wanna run a separate zone here and Im only going to put in a slave bypass kind of switch ( radiator section ), and this will either be "on" or "Off"). That area of the house is on a separate zone for the room from which the porch extends.

The outdoor design temp is some kind of averaged temp and it reflects the coldest day of the year, so it automatically calculates the worst case heat loss.

That seems like you could be dumping a lot of heat into a small area which will do two things; overheat the small area or unnecessarily waste heat. Why can't the slave bypass be run off a separate solenoid valve controlled by a thermostat in the sun room, FM?

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JTT

Quote:

Why can't the slave bypass be run off a separate solenoid valve controlled by a thermostat in the sun room, FM?

Try nthat again and make believe that Im your mom.

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farmerman wrote:

JTT
Quote:
Why can't the slave bypass be run off a separate solenoid valve controlled by a thermostat in the sun room, FM?

Try nthat again and make believe that Im your mom.

First, why a slave bypass? So you don't have to run pipe all the way back to the main manifold; is it buried in the wall, hard to get at. If you can, I'd run a new line from the main manifold if possible. Failing that ...

I'm not 100% sure what a slave bypass is, and I've never done hi-temp water heating though I've done radiant floor heating but can't the flow in any piece of piping be controlled/diverted at any point on the line with a solenoid valve that is then controlled by a thermostat that's wired in in the sun room.

The hot flow would go out on the hot side, that's where the solenoid valve would operate to divert flow and then a return line would have to be piped in on the "cold" return side.

Again, I'm not sure this will work. It just an idea, FM.

Have you thought about radiant floor heating. I guess it would be too late if the floor, concrete? has already been poured.

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we did consider radiant heat in another addition to our 250 year old farmhouse. It had requirements that we couldnt accept aesthetically.
When I mean a slave , its a loop that peels off the main heat loop that serves the studio (and this area already has a separate zone control. We dont want another zone because the house is already like a rabbit warren. These old homes were meant to be added onto as the family grew. We have several"wings" that in some cases are cellared and in others , only have crawl spaces.

I wish I had the ability to undesign and retrofit an entire new heating system with a logically run series of zone controls that could sense when people are in the zone and quickly heat up by radiant heat followed by conduction . (However, that aint gonna happen unless my Titanium ship comes in or my latest paintings sell for way more than their worth) :wink:

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farmerman wrote:

When I mean a slave , its a loop that peels off the main heat loop that serves the studio (and this area already has a separate zone control. We dont want another zone because the house is already like a rabbit warren. These old homes were meant to be added onto as the family grew. We have several"wings" that in some cases are cellared and in others , only have crawl spaces.

That's what I figured. So with a super insulated sunroom receiving solar gain compared to a ?well insulated? poorly insulated ?? studio, will your sunroom overheat.

I'd at least consider putting a ball valve on the hot side/return side ??? , ask your dealer, of the sunroom loop so that you can restrict the flow, sort of a hands on thermostat.

Good luck, FM, also with your titanium ship.

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BTU NEEDS

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