Comfort Part II, Ebels/ME

THP_3

Do you have a lap-top computer in your truck?
I still think your fishing for a new?

Mark Adams

Followup Design Stuff

Gang,

I recently posted a query on balancing cost vs. comfort and got 30+ great replies. Was super reading. But the last two messages from S Ebels and ME really got me thinking. Why? Because I thought that rad panels were simply too expensive! But after checking out hydronicalternatives.com I see that one style of panel would come to less than $200/room. But questions remain.

1. Seems that the panel ratings are for 180F water. Assuming I go with an Ultra or Peerless/Munchkin and work in radiant underfloor for the kitchen and two baths, shouldn't the rad panels be designed for 160F water? If so, how do I convert the output at 180 to output at 160? Maybe the data was on the website and I missed it. If I go insulated joist space for the radiant floors, the water temps for the panels and floors will be very close and I can hopefully mix down the water for the floors without any controls.

2. This is a 2200SF ranch in WNY with full bsmt. Rooms range in design heat loss from 1100-4600 BTU/hr with the house avg at 15-16 BTU/SF, not including the bsmt. If I have a room with a 13x17' room with a 4000 BTU/hr requirement and use a panel that indicates this loss at my design water temp, then that's it, right? Same as BB? Just match the room loss to the panel rating?

3. With a modulating condensing boiler, the best control method seems to be constant circ with what type of temp control? TRV's? Stats and zone valves? Comments?

4. Would all these rad panels be piped with PEX or PEX-AL-PEX? i.e. very little copper?

Hopefully, the 2nd ed. Siegenthaler book will be in my hands by tomorrow.

FWIW, I am a mechanical engineer and have did some heavy commercial HVAC in the late 90's, but this residential stuff with all the new hydronic gadgets and gizmos is fascinating!

Thanks,
Mark

Mitch_4

was on another post.

Here you go!

Mitch

S Ebels

One at a time.........

Item 1: Yes definitely design for lower temp water.
Use a factor of .71 for 160* supply with a 20* drop. That will give you the actual output of the rad at the lower temp. If you do the math you can keep playing with water temps, rad and floor outputs until you arrive at a common temp. My own preference is to aim for 160* at design temp with the underfloor limited to 140* via whatever type of control you choose. It can be a simple as a thermostatic three way valve.

Lets take your 13x17 room for example and assume you're doing a medium temp (<150* supply) suspended tube setup with a rad making up the balance. Your room is 221 sq ft and you'll get roughly 8-12 btu's /sq ft from the tube.(lot's of "it depends" in that hypothetical number) Let's use 10 for easy figuring. That gives us 2210 btu's from the floor. Now we can see that the panel rad has to make up a balance of 1,800 btu's.

2, A btu is a btu is a btu. Where the ones you lose get replaced from really doesn't matter.

3. Constant circ? Yep! TRV's? right again! Sometimes I will use the boiler output to control a zone relay panel which in turn runs the circ(s). This allows you to install a t-stat in the control scheme for use basically as a high limit and/or setback. Depending on the control you'll get DHW priority and WWSD also.

4. We use P-A-P almost exclusively for rad piping due to its much lower expansion rate. (think quiet here) Especially if it's going to have the potential to be an on/off system. The rads are usually run down through the floor or back into the wall with copper or steel and then attached to the PAP.

We get lots and lots of WOW'S and THANK YOU's from folks with these combo systems and I think they represent a very good blending of comfort, cost and simple control.

I'm sure Professor Eatherton will chime in here also.

Mark Adams

The load in the example

indicates that the standard 10-12 BTU/hr from the floor will not cut the muster. Got that. But what about ONLY using a rad panel? For instance, this 13x17 room is on the NW corner of the house. The 17' is W exposure with 2 medium awning windows and the 13' is on the N with 2 large casements. Slant/Fin HE2 tells me abut 4000 BTU/hr. BUT, will ONE rad panel be OK? Put below the northern windows maybe? This is a bedroom with carpet. The rooms slated for underfloor are the baths and the kitchen.

Thanks guys. I anxiously await the professors comments.

Best regards,

Mark

Mark Eatherton1

I concur...

for the most part! I think Steve hit the nail pretty squarely. The only additional thing I'd suggest is that you also remember to include a pressure activated bypass in your near boiler piping to accomodate the operation of the TRV's. Either that, or to maximize your energy savings, one of the new variable speed pumps based on delta P.

As for the room example, yes you can do it with a single radiator placed on the coldest wall. I've even done rooms where I couldn't put the radiator underneath an outside window at all, and the room still stays perfectly comfy.

As for design temps, I have no problem with the 160 design, but if you can design to a 30 degree delta T and throw everything in with an outdoor reset, you will spend 95% of your running time in the condensing mode, which will give you the greatest ROI.

As for the joist bay system, as long as you're going to do it, you might as well do it right and install some extruded heat transmission plates. You can use an Oventrop Unibox controller for htis and it will work great. Remember my comment about not wanting to hear your heating investment? Suspended tube and or staple up will be noisy. Plates will not.

PAP with a transisiton to copper prior to coming thorugh the floor work great too. It makes the pipes vacuum cleaner and kid on trike proof.

Congratulations on your invest in comfort. you won't regret it.

ME

S Ebels

One is just fine

Read number 2 on my list. It doesn't matter what is making up your lost heat. You can use one rad that fulfills the requirement or divide that load between 2, 3 or 6. Whatever your little heart desires. The number of rads is often based on customer preferences regarding location of furniture, windows, doors etc. Bottom line is if your load is 4,000, put in whatever it takes to hit that target.

My first reply didn't cover nearly all the variables that can be encountered and Mark brought up a good one with the PAB valve. When all the TRV's are shut down and you're still running constant circ, you have to provide somewhere for the water to go or burn up the circ. There are many other methods as far as your piping arrangement is concerned also. Siggy's book will help. Pumping Away by Dan shows some good basic arrangement of different styles which may or may not be needed in your house. Read and enjoy the world of modern hydronics.

Mark Eatherton1

And...

Welcome to The Wall!

Stick around, you just might learn something:-)

ME

Mike T., Swampeast MO

I've even done rooms where I couldn't put the radiator underneath an outside window at all, and the room still stays perfectly comfy.

Over in Europe where TRVs are standard and panel rads very common, they've done some recent experimentation with radiator placement. Found with reasonable insulation/infiltration control that some traditional ideas were backwards. Tall, narrow radiators on interior walls in full view of the exterior walls proved to have the greatest proportion of radiant heat.

All of the iron radiators on the 2nd floor of my 1903 house are on interior walls. The dead men even oversized them to compensate for what they assumed to be less-than-ideal placement. With TRVs and constant circulation, comfort level is great, the radiators are never hot and no draft problems despite an abundance of large, original windows.