Panel radiator system design options

DavesHouse

Hi Everyone,

I’m putting an addition on my house and now its time for a new heating system. Old part of the house has a massive oil fired forced hot air setup with some interesting ductwork. We just installed a gas line and I’d like to switch everything over to steel panel radiators with a TRV on each one, no central thermostat in the house. Total heat loss for everything is 40k btu/hr (house will be 1900 sq ft ranch). Room heat loss numbers range from 500 btu/hr (small bathroom) to 9500 btu/hr (living room).

The piping for the radiators would be 3/8 pex home runs to each radiator, 2 manifolds (13 or so total radiators), fed by an Alpha pump (or maybe a Wilo eco with its slightly lower curve). I’m currently sizing the radiators for 150° supply at design conditions. I’ll be having my plumber do the install but I want to make sure I understand everything and have the system set up how I want before the work starts.

My big question is which boiler option is the best-

Option 1- HTP pioneer boiler, run with outdoor reset and jump the TT. This is probably the easiest, no short cycle issues with the small zones. The boiler would just work to maintain the tank temperature. If there is only small demand the pump can pull warm water out of the tank without the burner firing.

Option 2- A low mass mod con (probably an HTP UFT-80) piped into a buffer tank. Not sure what the best way to control this would be, maybe a tekmar outdoor reset with a temperature sensor in the tank to fire the boiler? That way the boiler is just controlling the tank temperature as the system needs it. Outdoor reset would be disabled on the boiler and run through the tekmar. I’d need an additional circulator to feed the tank. Would this work? Am I missing anything obvious here?

Is there any large upside or downside to either one of these options? I like option 2 better because it gives me a better option to also run an indirect tank for DHW, but it is a more labor intensive install and I’m not sure if I’ll have any control issues.

I know this is probably over simplified so feel free to tell me where I’m wrong and what the better option would be. Thanks for the help

Rich_49

Where are you located ? What type fuel are you using , NG or LP ?

I would size the panel rads for 130 - 140 * at design allowing condensing throughout the heating season .

HTP used to produce a unit called Versa Flame . Basically a Pioneer with a FPHX , DHW mixing valve and a circ to make DHW . This unit can be produced on site relatively easily . Using a Taco i Series ODR mixing valve can also increase the capability of the Pioneer .

The UFT idea is a good one . I would configure this buffer as a 2 pipe buffer with the loads between the boiler and tank . Use a Taco Pc700-2 control and place the sensor in the tank . program that control and the boiler ODR the same . The only call the boiler sees is from the Taco . In this case you would need a Taco SR EXP unit to use with the 700-2 . Indirect aquastat would go to priority and priority end switch would go to DHW terminal on UFT . This would cut power to CH circs during a DHW call .

All things considered the Pioneer option is similar in cost but less complicated .

DavesHouse

Thanks for the help!

I'm in MA (zone 5), just put a NG line in the house so i'll be using that. I'd like go lower with the supply temperatures, but there are some spaces that don'd lend themselves to larger radiators easily.

Using the reset curve on the tank controller along with the boiler makes sense so it's getting the right temp for supply water. Would the indirect sensor need to be connected to the switching relay, or could it just go directly to the boiler? It looks like the boiler will prioritize DHW on its own. Not even sure if i'd hook up an indirect tank, but it would be a nice option to have. I currently have heat pump electric water heater that is pretty recent.

I do like the versa flame, but it seems like it is quite a bit more money than the pioneer. I like the pioneer option for plug and play, but I think a seperate boiler and tank would give me more options and be easier if a component fails.

Thanks

Rich_49

The DHW sensor would have to go to the Taco relay in this scenario because we are relying on dropping the CH circs out . You could connect directly to the boiler , however the CH circs would continue to run and pull water from the boiler while a DHW demand is present

DavesHouse

That makes sense, thanks!

DavesHouse

Any other thoughts out there? Is there anything i should consider doing different?

Thanks

Rich_49

You're on the right path . Explore your options based on your budget but the theory is sound

Brewbeer

Also take a look at cast iron baseboard. It holds quite a bit of water and will act partly like a buffer tank. If you can install enough of it, you may find that you don't need a buffer tank.

DavesHouse

I looked into the cast iron baseboard, but it looks like I can get the radiators for a lot less money. I had the radiators in my last house (with a completely different system) and was happy with them, so I don't want to mess with success.

I keep coming back to the HTP Pioneer from a simplicity standpoint- it seems pretty foolproof. How well does this unit work for DHW with a FPHX? I'm assuming i'd have to raise the lower temp limit to 130 or something and maybe use a mixing valve to supply the radiators so I can supply cooler water when the outdoor temp drops. I can see this being very efficient in the winter when the heat is always running, but is it still cost effective in the summer to keep the entire tank heated just for DHW?

I dont mind my electric heat pump water heater, but i'd like to at least set my system up now so that i've got a good option to heat the water with NG in the future.

Thanks

DavesHouse

One more question- If I went the UFT with a buffer tank route, is there any significant advantage of a 2 pipe over a 4 pipe buffer? I've been reading up on it and cant make my mind up one way or another

Rich_49

2 pipe is a far better option . Pioneer does a damn fine job making DHW with a FPHX . The only reason that HTP discontinued is a lack of sales of the Versa Flame . Just to be clear you'd be making a Versa Flame using the Pioneer , FPHX , mixing valve and circ .

Boon

I'm curious about the use of 3/8" pex. Won't the 3/8 be an 'unnecessarily' high pressure drop?

Rich_49

3/8" tubing can be used to our advantage . Too low pressure drop presents a larger problem . There are a handful of design days a year , if 3/8" tubing can keep you warm during that time what issues does it present ? Let's look at those whole bunch of other days when your gpm , feet of head decline . The circ whether on a zoned system or not may very well operate below the performance curve . You very well may end up moving 4 gpm when you need 1.5 gpm ( pump affinity laws) .

Question . Would you rather operate the circ to the high end of the best efficiency point for a small part of the season or on the low end of the best efficiency point for a large part of the season .

Keep in mind , when you are on the low side , moving 4 gpm as opposed to 1.5 you are also sending hotter water back to the source and as such are delivering less BTUh . Make sense ?

Rich_49

This is from another discussion taking place on another forum right now . Call me crazy if you'd like but never refer to Bean as a nut .

Robert Bean

Consider:> 50% of construction projects in North America are < 20,000 sf. with over ½ of those under 5000 sf. + long term trend is reducing loads through increases in building efficiency + the greater the building efficiency the lower the flows + the lower the flows (generally) the less horsepower required thus the greater the risk for both oversized circulators and control valves + excessive flow is one of the major areas of waste in hydronics = clients paying for anything oversized are paying for something they don’t need and will never use...ever! ...…and be aware that street pricing of product can distort one time capital cost evaluations…but not life time operating costs. No surprise I'm with Bradford E. White (again) on this one...shown below is one comparison from our integrated design course. You may not like the compassion so do you own on your next project...rarely will you find zoned circulators beating valves when it comes to power...
Manage

Rich_49

https://www.facebook.com/groups/630821090438762/?multi_permalinks=994305040757030&notif_id=1519162156940531&notif_t=group_activity&ref=notif

DavesHouse

I'd like to use 3/8 pex for the pumping reasons that Rich mentioned. If i'm running the radiators in home runs off of the manifolds, each radiator is its own zone and the largest is not even 1 gpm at 20 delta T. With 1/2 pex i'd be well below the minimum head curve for most pumps.

Rich_49

In Europe they even use 5/16" tubing . Nothing to be leary about using 3/8"

HVACguyinME

@DavesHouse

Not sure if you have tried the IBC SL boilers but they have a control that can ramp heat up so if one of your small rads is the only one calling the boiler can ramp at .6 degrees an hour all the way up to 26 degrees an hour. Firetube heat exchanger like the UFT and you can even put the control online with a cat 5 cable hooked to your router.

DavesHouse

Thanks for the suggestion of the IBC, it looks like it has an integrated secondary circuit sensor that can be put in the buffer tank so no additional controls would be needed. Not sure how the availability or pricing is near me, but it looks like it might be an easy solution.

Thanks

DavesHouse

So as i think about this more (or overthink it) i've been looking at some of the threads with systems designed off of a water heater (HTP phoenix or similar) using a FPHX and an outdoor reset mixing valve for the radiant. This seems like it could be much cheaper and less complicated than a boiler, buffer, and indirect tank.

What are the limitations of a system like this? Is 40k btu at design conditions too much? (only 4 gpm at 20 delta t, so it doesn't seem too bad from a heat exchanger perspective). There wouldnt be any short cycling issues with constant circulation for the panel radiators. What point is there a big trade off in efficiency for a system like this compared to a standard boiler setup?

Thanks

Eastman

Why do we want a buffer for a TRV'd panel rad system?

DavesHouse

I don't think I have much of a choice with the buffer based on every radiator being zoned individually. I'm sure there would always be some amount of flow with the thermostatic valves but I don't know if it would meet the minimum boiler flow requirement or minimum btu level. Somebody please correct me if I'm wrong.

Rich_49

Eastman said:

Why do we want a buffer for a TRV'd panel rad system?

Because , no matter what the emitters are there will still be times when the load is much lower than low end modulation . Maybe I misunderstood your question ?

Rich_49

Dave asked

So as i think about this more (or overthink it) i've been looking at some of the threads with systems designed off of a water heater (HTP phoenix or similar) using a FPHX and an outdoor reset mixing valve for the radiant. This seems like it could be much cheaper and less complicated than a boiler, buffer, and indirect tank.

What are the limitations of a system like this? Is 40k btu at design conditions too much? (only 4 gpm at 20 delta t, so it doesn't seem too bad from a heat exchanger perspective). There wouldnt be any short cycling issues with constant circulation for the panel radiators. What point is there a big trade off in efficiency for a system like this compared to a standard boiler setup?
No limitations with the Pioneer . No minimum flow requirements . Mass to leverage in a nice way . Size the FPHX to your needs . ODR onboard for winter summer temp for DHW
I Series ODR for heat and just sipping out of a 55 gallon cup . 1 circ for DHW and 1 for space heating . LOW MAINTENANCE . All sounds good to me .