Design a simple system

Gene Davis_3

I'm not a heating pro.  A retired engineer, I enjoy making a little spare change doing designs and construction documents for new construction and remodeling.  I enjoy knowing something about the heating systems, however, and have been involved in a half dozen or so new builds with various forms of radiant heating.

A small vacation home is being cooked up on paper, and is proposed to be heated with panel radiators (TRV-equipped) throughout, using a small mod-con wallmount like a Trinity Ti (good local service), fired with LP gas.

Crawlspace with the mechanicals there, a 950 sf main floor above with 5 radiators, and a half-story above that with 3 more radiators.  Main has foyer-entry-kitchen all one fluid space, then a bath, laundry, and bedroom.  Up has two beds and one bath.

Zones?  Outdoor reset?  One wall t'stat only, somewhere on that main floor?

I'm curious as to how this might best be laid out.

CMadatMe

Simple

Just designed a job this way. Used a mon-con. We used a Wirsbo True Flow 7 Loop radiant manifold supply 7 integral panel rads. No thermostat! There's a nice diagram in the attached on page 19. Take a read.

Gene Davis_3

Wow! Great information.

Looks ridiculously simple!  Thanks a lot.

Appears to be a "control board" even a retired engineer can pipe and understand.

CMadatMe

Glad to Be of Help

Make sure you do that heat loss and make sure you use the manfactures correction factors when sizing. Some only give you the 160 degree water rating.

Gene Davis_3

Could it really be that simple?

Thanks again, Chris, for your remarks and the link.



Could this really be that simple?  A regulated variable-speed circulator, just one, simple outdoor reset, the manifolds, and panel rads each equipped with a TRV?



No primary loop, no closely spaced tees, no monster of a control board?

For the large common part of this small house, its foyer-greatroom, kitchen, hall-adjacent-staircase, the radiator array will likely consist of three units, and I was going to consider them as really one zone, piped on the same loop from the manifold, and with a TRV on only one.



Howzzat sound?



I'm just trying to get a handle on this, for my own interest.  At real system design and build time, we'll engage a pro, but I like advice from the pros here, so that I am well-informed.

CMadatMe

Using a Mod Con

We used a Low Loss Header/Hydro Seperator, Grundfos Alpha as a system pump and a Wirsbo Radiant Manifold. Make sure the valves for the rads have a bypass in them and it's simple as simple can be.

Simply Rad

almost there

Why not take it one step father and over size the rads for a 140 degree supply during design conditions.  That Trinity will be spitting the condensate out and saving of $.  That way you can spend more time at that vacation home.  I am not sure about Trinity but the mod/con we use has the ability to turn the system up and down(home and away) with a phone dialer...perfect for a vacation cabin.  The phone dialer even has a sensor for freeze protection.  We have also had great luck with differential pressure pumps with this type of continuous circ system and TRVs.  We have used both Wilo Stratos and Grundfos Alpha.

The systems are incredibly simple, comfortable and efficient.

Happy Holidays

Jeffrey

Gene Davis_3

There, with bigger rads sized for 140 F.

Great advice so far from all, and thanks!

We'll look into dialup control, but in the mean time, I would like some advice on the look of the system.  What is to be changed, in the image attached, when a mod-con is used?

Will we want a primary loop, closely spaced tees, and from those supply and returns, do that manifold arrangement with the pressure-regulated circulator, and a temp feedback device just downstream of the circulator, to report back to the boiler?

Simply Rad

Heat loss

As said before do the heat-loss and then design the rads around your loads.  The heat loss will dictate your flow-rates.  Generally speaking the rads require low flow rates.  You might be able to pipe the system exactly as your drawing.  First look at the boiler's specs on flow-rates vs pressure drop.  If you can,size the circulator for both the boilers specs and the rads together.  As you know the boiler have certain flow characteristics as do the rads, BUT in simple cases you might be able to get away with just the primary loop.  Normally we use a low-loss header to separate the boiler from the distribution system.  But in simple systems we can get away with a system like your drawing.  Just do the math. 

If the trinity has a boiler sensor then install it just downstream of our DP(differential pressure) pump. 

One more thing about mod/cons.....They require maintenance and service!  They can  burn efficient and clean if they are maintained.  Also, service is being proactive instead of reactive.

Happy Holidays

Jeffrey

Devan

reverse return

the manifold is also an option.

Charlie from wmass

Good point Devan

While the manifolds are nice for zoning control with radiant floors or ceilings it is redundant for a trv system. revers return and trv's and you would have a very dependable and efficient system. I would say if you did not use the mod con then a hydraulic separator with a cast iron boiler and then you can run the rads by outdoor reset and keep the boiler at none condensing temperatures. If you go with the mod con then you want it to run as cold as you can to gain that phase change energy.

EricAune

Not sure why that would matter

Maybe I am not seeing it, but reverse return on a manifold system with TRVs would do nothing as I see it.  Flow through each loop is dictated by the trv.  I use manifolds for baseboard applications as well, can't see why it would affect the operation of the system to reverse the return there either.  Flow through individual loops should be balanced at the manifold adjustment valves, this adjustment is dictated by the length of that loop.



Enlighten me please if I am wrong, but I see no benefit to reverse return on a manifold system in any application.

Gene Davis_3

Reverse return? How elegant!

Wow!  What great advice I get here.  Thanks!

A single supply line with taps up to each radiator, all rads TRV-equipped, the supply line ending at the furthest one out.  Reverse the scheme for the return, as per the diagram attached here.  That simple?

And for the circulation and control, run it with a pressure-regulated-circulator and control via the outdoor reset, as shown in my earlier diagram?

Here is a question I thought I asked earlier.  Part of the house is one large common space (kitchen-foyer-LR-DR) and it will require three or more radiators.  Should EACH ONE get a TRV?  Or should we just do one of them with the control?

Charlie from wmass

Reverse return

Eric if you are using trvs why use those manifolds? if you reverse return it will help balance the flow without needing to spend time fiddling with those valves. You also have a chance to make extended manifolds to better balance flow and reduce the footage of pex and stream line the boiler room.

Gene as far as I can see a true reverse return looks better on paper than on installation But it can be done to a certain level. The radiators will each need a trv unless you decide one will be always on. If you are running the system on constant circulation with a pressure regulated circulator you could leave on radiator in the great room without a TRV.

CMadatMe

How About Some

NIce decor style rads for the living space and reg rads for the bedrooms. The decor rads are avail in different colors and may fir in nicely with the decor of the room. There are also accessories, like shelves, coat hooks etc. See the attached.

Vinca would be really nice in the entry way and possible the Carre 1/4 or 1/2 rounds for that vaulted area.

NRT_Rob

you need a bypass

with a mod/con if you do primary piping only. Thing is, with only 950 sq ft, you might have a hard time with short cycling on the boiler if you use one.



You probably want some kind of buffer tank.



You probably also want at least one master "kill switch" setback thermostat so they can turn the house down when they go on vacation without fiddling with 8 radiators.

NRT_Rob

you're correct

reverse return only works when you are doing long headers and trying to equalize out the pressure drop in the header itself.



however, flow balance manifolds are still good for TRV systems. if you hit your reset curve and radiator sizing appropriately, you may have the valves nearly fully open most of the time. Or if you use any kind of setback setup.



Having individual isolation just for purging is nice too.