Newbie here looking for suggestions on system design of the baseboards.

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Old 07-11-12, 09:22 PM
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Newbie here looking for suggestions on system design of the baseboards.

Hello all,

In a residential house with a boiler outputting 180F is it better to connect baseboard in series or parallel? Most installations that I have seen are connected in series. To me this seems simpler to install but not as efficient as a parallel install.

Going back to my Thermodynamics class (which I squeaked by) more heat can be transferred with a greater temperature differential. Also more heat can be transferred with a slower flow rate. That is where I am swayed by a parallel baseboard install. The inlet temperature would be the hghest for all the baseboards and flow would be roughly divided evenly for all the baseboards.

Open for any input.
 
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Old 07-12-12, 05:03 PM
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Hi 2mile, welcome to the forums...

I'm not really sure how to go about explaining this... as you've mentioned 'efficiency' and technically that's not really a correct term. ' EFFICACY ' might work for the semantics, but it really doesn't mean anything as far as saving money.

I'm simply going to say that a SERIES installation is the way to go simply for the reason that the cost of doing otherwise is ridiculous... in COPPER anyway... if you are going to use O2 barrier PEX, I guess it could be cost effective, but there's really no point.

If you are designing a NEW INSTALL, has a complete ROOM BY ROOM heat analysis been done?
 
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Old 07-12-12, 06:52 PM
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Take troopers advice.
To clarify flow and heat.
Also more heat can be transferred with a slower flow rate
Slower water will drop the temperature in the water more than a higher flow rate but more heat (btu's) are transferred on higher flow rate.
Check baseboard charts, more btu output at higher flow rates. If you want to heat the home faster speed up flow making sure not to exceed 4 ft per second and not be slower than 2 ft per second.
See a chart here.
gpm
Check any water temperature and compare 500 lbs per/hr (1 gpm) and 2000 lbs per/hr (4 gpm)
 
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Old 07-12-12, 09:28 PM
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I understand efficiency as (heat out)/(heat in) * 100%. That comes from my Thermodynamics class. Moot point.

A heat calculation was done. The system will be a four zone system for a 2000 ft[SUP]2[/SUP] house. The first zone is for the kitchen/living room and needs 30,000 btuh. The second zone is for the master bedroom and master bathroom and needs 7,800 btuh. The third zone is two bedrooms and the other bathroom and that needs 10,200 btuh. The forth zone is for a future attic build that measures 400 ft[SUP]2[/SUP].

I am using pex, the house is a new build, and plumbing the baseboard heaters series or parallel is doable.
 
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Old 07-12-12, 10:06 PM
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So the basic heat transfer equation from mass flow is

Q = [m x c[SUB]p[/SUB] x (Tout Tin)]

where Q is heat transferred, m is amount of flow, c[SUB]p[/SUB] is the specific heat of the liquid, and T is temperature of the liquid.

The equation uses measured quantities (flow rate and temperatures) to get an answer.


Effectiveness is what I meant, not efficiency. It has been 18 years since Therom class.
 
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Old 07-13-12, 06:29 AM
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I clicked on the link and I'll use the numbers.



Say I have 4 baseboards that are in parallel and a pump that can supply 4 GPM. With a working fluid at 180F, there would be 590 BTUh for each baseboard because the flow should divide fairly evenly. This would net a total of 2360 BTUh.

With the same setup as above but the 4 baseboards in series, I'll assume a 5F drop in temperature after each baseboard. The first baseboard would make 620 BTUh, the second would make ~585 BTUh, the third would make 550 BTUh, and the forth would make ~515 BTUh. So all four baseboards would produce 2270 BTUh or about 4% less than the parallel.

I did make some assumptions so the difference between the two types of systems is marginal at best.
 
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Old 07-13-12, 02:48 PM
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You're actually overthinking the process.

In order to determine the correct amount of baseboard in each room, you need to know the heat loss on a ROOM BY ROOM basis. It is not enough to know the total for the zone because you may end up with not enough heat in one room, and too much in another.

For example, the Living Room is calculated at 10K BTUH. You need to be able to replace that heat loss. So, if installing baseboard that is capable of outputting say 550 BTUH / Lineal FOOT with 180F Entering Water Temp ( EWT ), you would need to install roughly 18 feet of baseboard in that room.

You need to continue this process for each room until you arrive at the correct amount of BB for each room.

Once that is sorted out, the next thing to understand is that if you are running 3/4" tubing with a flow of roughly 4 GPM, (which is more or less the 'standard') you can extract roughly 40K BTUH from that 'circuit'. What this means is that you need to design your zones such that no single zone is more than roughly 65' baseboard.

In general, heating systems are designed for a 20F Delta T. The ENTERING water to that loop can be 180 but of course the LEAVING water will be cooler, by as much as 20F. It does not have to be 20, it can be 10, or even less, but generally should not be more than 20. So you can have SHORTER loops with no problem at all.

The next step is to understand that as the water cools around the loops, the ENTERING water to the furthest rooms along the loop will be less, so you need to compensate for this by adding a few feet of baseboard to those rooms. There are charts available that show the heat output at various water temperatures. Use those to determine how much extra you will need.

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Old 07-13-12, 02:58 PM
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I don't recommend using the MAX numbers for BTU output that the manufacturers provide. Reason being that they are 'perfect world' numbers. A light coating of dust on the fins can make a pretty large difference in heat output. Heavy furniture in front of them will cut it down. In other words, derate the manf output rating by 10% or so.

There's really no need to look at parallel piping... I personally think there is nothing to be gained in terms of performance. Properly designed series piping is SO much easier, and even using PEX will save $.

You want to add some extra heat to the bathrooms. So don't skimp there. Think about panel radiators in the bathrooms, or even if you wanna get a bit fancy, heated towel racks. You don't want anyone complaining about the bathroom being cold!

Effectiveness is what I meant,
Right, EFFICACY.

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Old 07-13-12, 02:59 PM
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I wanted to figure out what was the better installation was. Series wins with the ease of installation.

NJ Trooper - thanks for the GREAT info
 
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Old 07-13-12, 03:02 PM
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You don't HAVE to design for 180 water!

The cooler the water that you can heat the home with, the more economical it will be.

With a conventional boiler, you don't want to go TOO cool and risk having issues with flue gas condensation, but you could certainly design for 160 water.

All this means is that you have to install a couple extra feet of baseboard PROPORTIONALLY to each room. You will have the heat emitter output that you require at a cooler water temp and save a few bucks on fuel in the process. Yes, the cost is slightly higher up front, but that will pay for itself in a few seasons.

There are piping schemes that would allow you to run even cooler water in the system, but these tend to get complex and you seemed to indicate that you wanted to KISS.
 
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