Help with a design

347

Hello All,
I'm have a little trouble(pulling a blank more like it) laying out a radiant job.
I'm installing an entire house(three floors) of radiant. As per the radiant design I need two temperatures for wood and tile. I'm also installing two fan coils for a quick/back up heat for the house( the house will only be used parts of the year). The boiler will be a Buderus GB series with an 80 gallon indirect w/h. Going to add a buffer tank because of small zones. The owner wants every room(13) zoned, I got him down to three per floor with the option to change them at a later date if he wants. I'm installing 3 manifolds on each floor with zone heads to make it easier to break up the zones if necessary. The basement and first floor are simple to do. The problem is getting piping to second floor manifolds(that's another story). I was thinking about installing 1" PEX(loop) from the boiler in the basement up to the attic(above the second floor) and take a three sets of tees off loop and doing a P/S off them, installing a circulator in the basement for the 1" and three in the attic for each manifold. I would have the basement ciculator(primary) turn on when any zone comes on. I'm also mixing down the water temperatures with Taco RMB's.
Any help or comments would be appreciated.
Thanks

Rich_49

So are you using circs or RMBs ? Go to Taco FloPro neighborhood and look at the zoning for radiant webinar .
Mixing is an expensive option when you are using many zones and temps . Let your highest temp drive the system and ODR curve . zone away properly , when the floor surface reaches the required temp at differing loads the stat will satisfy and flow will stop . No flow , no more heat .
I really do suggest you watch that webinar or read the PDF .
You are sounding like you are not too sure about the things you speak of . RMBs are an injection loop and P/S right out of the box . It sounds to me like you are about to get into alot of trouble . Ask for design help or pay someone qualified to do it for you . Don't let the people you purchase from decide what you need , bad idea in most cases , there are a couple qualified Reps and wholesalers but not many .

347

Thanks for the quick response Rich.
My mistake, I was going to use the RMB's pump to get the mixed water to where it needed to go(the attic loop) and then use circulators(P/S off that loop) to work the radiant manifolds. I guess my question to you would be how do I get the two recommended water temperatures(95 & 120) for the radiant zones if the boiler is firing for high temperature(160 plus as per the HVAC guy) for the fan coils? I don't want to over heat the floor during that time. I thought the RMB's would reduce the temps to what I need and the buffer tank would stay at the higher of the three water temperatures needed.

Rich_49

Fan coils can also benefit from ODR , why use 160* all the time ? Maybe your HVAC guy does not understand that the CFM never change since the house is always the same size , loads change based on outdoor temp so changing the water temp to the coils makes sense . Ask the HVAC guy what brand , model coils he is installing . I am always amazed when the best HVAC guys in the area send 160-180* fluid to a coil with an aquastat set at 110* on -130* off . Kinda makes you wonder ,
* What is the boiler make and model ? What areas do the hydro fan coils service ?
* You would do yourself a favor by using Taco I Series odr mixing valves and pumps only . Save your money on first cost and monthly electric and aggravation .

gennady

Here is my 2 cents. Do not use thermostats for radiant heating. Use in-floor (slab) sensors. Also, if, you are going to zone radiant, you need to set up different ODRs for each zone.

Rich_49

You could do what Gennady says also . Of course you must remember that all floor radiant does not have a slab , different rooms have different BTU sq.ft requirements , different finish floor R values , different use patterns and quite possibly greatly varying SWT requirements . This could get rather complicated and expensive . Then again , how is it that a slab sensor meant to protect the floor from overheating will read MRT within the living space ? So when you require only a 75* surface temp you may possibly get 85* , Now that's comfort !
* Remember to place rooms on the same zone they must have similar characteristics like the ones mentioned above . Slabs are not the best way to do radiant and have not been for quite some time , some still like them but they are a PITA . Mass has a new address and this OP has already determined that address , at the buffer tank .

gennady

In my understanding on how radiant is working, room temperature has nothing to do with comfort and unless it is low heat loss space RT will be lower than 70F. Otherwise radiant is not the best option and other ways of space heating must be applied.

SWEI

Air temperature has something to do with comfort, maybe 25% IIRC? MRT is more like 65%. Anyone happen to have a cite for those numbers handy?

gennady

When heat loss is more than radiant can provide at design outdoor conditions then I offer axillary heat to complement radiant. I can't agree more that RT below 65-66F is uncomfortable. But I would not bring RT over 70F max in radiant applications and this is unavoidable in low heat loss spaces.

Rich_49

Closest thing I can think of Swei . By the way , I hope you all were able to detect the Sarcasm in the "now that's comfort" .

347

Thanks again everyone,
The boiler will be a GB142/24 the house has a total load of about 64,000 BTU's, I'm not sure about the coil type, he is hard to get in touch with. The coils serve the first and second floors, the purpose of the are to heat the house up quickly when the owner decides to visit the home. He will be able to control the heating system remotely, so he set back the heat when he leaves and turn it on when he is on his way. Since the system will take awhile to recover he plans on using the fan coils to heat the home fast and then let the radiant do its thing. The radiant was sized for each room(which all have the same floor covering). I was just running the loops to a central manifold in case he wants them broken up at a later time. As for the floor sensors he has been talked out of them by someone( I could not change his mind) and since he is paying the bills I just do what he wants. So in your opinion I should use two Taco I valves with circulators and let the boiler ODR control the fan coils?
What is your opinion about the P/S up to the attic to feed the manifolds?

Ironman

Your getting some good technical advice already, so can I add a little non technical: don't let your customer direct you in the technical design of the system - that's your job and what he's paying you to do. If he doesn't trust your ability to design it, then why did he get you to do it?

Ive had to deal with ones like you have before: they have just enough technical knowledge to be dangerous, they demand unreasonable things ( like every room zoned), and then they will want to hold you responsible when their design demands don't work correctly.

Unfortunately, you should have been firm with him before entering into a contract and politely stated that it had to be your design if he wanted you to do the job. Now, the best thing you may be able to do is put in writing that since he's insisting on his design, that he's totally reonsible for the performance of the system. Getting him to sign it may not be possible, but give it to him whether he will or not. At least this way you've got some documentation to cover your 6.

Again, be tactful, but firm. He can't have his cake and eat it to.

Tinman

Well said, Bob.

347

Thanks for all your responses, they were helpful.
Happy new year