New Hydronic Heating Design
Hey guys! Hope everyone had a Merry Christmas! I'm renovating a home that was built in 1936, currently it has a hot water boiler with one heating zone for the entire house and uses cast iron radiators in each room. For the renovation I'm planning on dropping almost all of those cast iron radiators and using baseboard radiators for some rooms, and radiant floor for others. I did heat calculations for each room and selected appropriate sizes of baseboard heaters. Also the house will be broken up into four different zones (2nd story = 1 zone, first story = 2 zones, and basement = 1 zone) My question is in regards to the pipe system design: Would it be better to do series or parallel pipe network for the system? Also the pipe fittings for the baseboard heaters are 1/2 NPT, would their be any advantage in using 3/4 piping and reducing / expanding at each fitting for the radiator? The baseboard heaters selected are Runtal Model UF-2, I wasn't able to find any specifics regarding head loss values for these, I was wondering if there are some typical values one could assume, or would it be best to contact the manufacturer? Any help is appreciated! Thanks, -Jim in my opinion it would be better not to do series installation. The increased pipe size would not hurt either. Runtal baseboard may be used with fin-tube, but the fin-tube will perform better if the Runtal is at the end of the loop. l Runtal is compatible with cast iron baseboard and cast iron radiators. l In series installation: an individual loop should not exceed 30,000 Btuh or 7 radiators the problem with using different types of heat emitters is that is may be hard to balance the sytem and get good results in all areas. one other hting to rememnber is if you are using any type of outdoor reset control on the boiler ,you may want to look at the designe of the system components may have to be upsized a bit ,especially in larger rooms, to give a a nice even heating result. What type of boiler are you using? If a mod/con I would keep the radiators for water volume, radiant output and comfort. Be careful not to micro zone the home as it will become detrimental in heating costs. I would do parallel pipe so all heat emitters get the same temperature. If you do series you will need to reduce calculated water temps when calculating the amount of radiation to keep the same air temp in all rooms. The system is normally designed with a 20f delta-T. So if at OD design you want the system to heat at 160f, 140f, 180f pick a number. When you hit that water temp is when you will have the design delta-T. So lets assume you want 160f at OD design. In a series circuit you will get 160f into the first radiator and maybe 16f less water temp in the last radiator. So the rooms at the end of the loop will need to have more radiation to meet the heat loss of the rooms prior on the loop. A parallel system will get the same water temp into all radiation. As far as pipe sizing a 1/2 line will carry 17k btu's and a 3/4 will carry 39k, normally rounded up to 40k btu's of heat. Radiant floor heating may not be enough to supply heat on it's own. You need to calculate the heat loss of each room to make sure you have the appropriate amount of radiation installed. You also have to be careful not to mix different types of radiators on the same zone because they provide heat differently and can lead to uneven heating. If you are in eastern PA, I may be interested in the radiators you are getting rid of. droo made a good point dependent on windows, insulation etc. The maximum you can get out of radiant is about 33 btu's per sq ft. Use the sq ft of the room and multiply it by 33 and see if it matches or exceeds the heat loss for the room. If yes than move forward. If not either reduce the heat loss or use another type of heat emitter. I'm not sure I would be adventurous enough to design around 33 BTU/SF ... myself would use something a bit more conservative... maybe 25 BTU/SF ... On a tile floor ... maybe I would count on 33... but a living room... or a bedroom... wall to wall carpeting, large furniture... these things will decrease the output of the floor assembly. I guess that the bottom line is to be very careful about the design, and know the limitations... it would be a bad thing if you did all that work and ended up with cold rooms. IMHO dropping the radiators is a mistake. Runtal's are nice but... you are getting into the range of needing a two-temperature system. That's extra control, mixing, etc. Radiators and radiant are two of the best emitter types for high-comfort and high-efficiency. The radiators and radiant could potentially all run one water temperature if you do your design/sizing right. The added volume of the radiators could also help mitigate short-cycling. If you can do one zone per floor, that would be great. On the floor you want two zones, consider a home-run or split loop arrangement and use thermostatic radiator valves. That will also improve comfort and keep the water circulating. Thanks for all the responses everyone! I'm definitely going to be using a parallel installation to help deliver the same water temperature to all radiators. Additionally I'm leaning towards dropping the additional zone on the first floor, making there be a total of three zones, one per floor. @drooplug @NJ Trooper: Yes I already have that on my list of things to consider about radiant heat, the only room I was planning on using that for wast the bathroom on the first floor which would be in zone 2. I haven't gotten to the calcs for that zone yet, but when I do i'll be sure to consider the 25 BTU/SF. The good thing about the remodel will be that new insulation, and double pane windows! @xiphias: The only think I dislike about the cast iron radiators are their size. I've read a lot of great reviews about the Runtal's. Runtal does say that the UF-2 baseboard models, can work with radiant floor heat, and as low as 140f. Do you think it would be that terrible of a decision to replace them? @rbeck: The boiler decision hasn't been completely finalized yet. I was looking into and heavily considering mod-con boilers. You said that you'd recommend keeping the radiators for water capacity... Would a mon-con boiler not be ideal for what I plan on doing with runtal baseboards, and a radiant floor? I also would like to use an outdoor reset control too. -Jim radiant heat, the only room I was planning on using that for wast the bathroom on the first floor which would be in zone 2 One thing to keep in mind in a bathroom is that you generally want it to be warmer than normal when in use... just thinking about standing around wet and nekkid on a cold tile floor gives me the chills! Use the radiant for just heating the room when not in use, and supplement when in use. Infra-red Heat lamps are nice for instant heat... they make combo IR lamp, vent fan, light units... and there are also ones that have fan forced electric heat... maybe something like an electric baseboard, or under cabinet kick-space heater... maybe a nice heated (by the hot water) towel rack?... Since this is a remodel, now is the time to do it! Just found this page that pretty much summarizes the options: http://www.bathheat.com/Electric%20H...ng%20Guide.htm Originally Posted by NJ Trooper One thing to keep in mind in a bathroom is that you generally want it to be warmer than normal when in use... The old-timers around here would put cast-iron baseboards all around the outside walls - except in bathrooms: then it would be half again or double that length. Worked out pretty well. The decision of using a mod/con before the radiation allows you to maximize the efficiency of the mod/con. Use design temps of 140f maximum. This will use more radiation but keep the boiler condensing all the time it is operating. If using a cast iron boiler you can use higher design water temps and use less radiation. Keep in mind that size the boiler off the heat loss and use the boiler DOE output, pipe them properly and both will benefit from ODR controls. The mod/con will have it included. If you want the radiant in the bathroom just to keep your feet warm, then you can probably install the right sized radiator to make up for the lack in floor heating. Originally Posted by NJ Trooper One thing to keep in mind in a bathroom is that you generally want it to be warmer than normal when in use... just thinking about standing around wet and nekkid on a cold tile floor gives me the chills! That is definitely one important details that would have been more than likely overlooked!! Thank-You!! I noticed the heated towel racks on Runtal's site whenever I was checking out the baseboard heaters and they definitely have an appeal! I'll have to think more about it though. But I'm checking out that article you sent. I feel like some IR lamps would be a good supplement to the radiant heat for when the room is occupied!! Originally Posted by rbeck The decision of using a mod/con before the radiation allows you to maximize the efficiency of the mod/con. Use design temps of 140f maximum. This will use more radiation but keep the boiler condensing all the time it is operating. If using a cast iron boiler you can use higher design water temps and use less radiation. Keep in mind that size the boiler off the heat loss and use the boiler DOE output, pipe them properly and both will benefit from ODR controls. The mod/con will have it included. Thanks, I'm definitely going to research the mod-con boilers a little more. Do you know of any good sources online that provide some really good design guidance of forced circulation hot water systems? I've basically just been using my knowledge of fluid mechanics and pipe networks on top of visually inspecting the previous system, but I think it would still be nice to get some more guidance. Thanks, -Jim Look under the Hot Water Boiler Info menu Technical Menu
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