Input on Single Zone P/S Radiant System Design

mopar440_6

When I built my shop 9 years ago I had tubes placed in the floor with the intent to complete the system later. I have designed and redesigned the system every year since but the time has come to make my building comfortable in the winter. Goal is to have as efficient a system as possible while remaining within a reasonable budget.

Building - 50x60x14 pole building in south central Pennsylvania
Insulation - 2" foam board below 6" slab and perimeter, R22 in walls, R40 in ceiling
Radiant - single zone, 9x 321 ft. (avg.) loops 1/2" pex, staple down (bottom of slab)
Design parameters - approximately 61k-70k BTU/h, 120 degF SWT, 20 degF. deltaT, 6.15 total gpm, 8.5 ft. head loss., 1" copper piping primary/secondary loops, outdoor reset will be used

Plan is to use a Navien NHB-080 (or is a NHB-110 needed?) boiler unless a comparable propane mod-con that is more readily available is suggested. Boiler will control both pumps. Honeywell T6 hydronic with slab sensor to control boiler.

Any suggestions to make the system more efficient, less complex, or reduce costs are appreciated.

Ironman

If the boiler has a fire tube HX, then it probably doesn’t need to be piped p/s as long as you have only one zone.

hot_rod

The Navian manual will show the minimum flow the boiler needs. As long as all loops run, you probably have sufficient flow to not need hydraulic separation.

Are you using glycol, be sure to factor that into the pump sizing. 35- 40% should be fine, if you use a good quality, not diluted, glycol.

mopar440_6

Ironman said:

If the boiler has a fire tube HX, then it probably doesn’t need to be piped p/s as long as you have only one zone.

Navien NHB series are water tube HX. Cost for an equivalent fire tube boiler is nearly as much as my entire system as currently designed.

hot_rod

Your drawing is about as simple as it gets and covers all the bases. You do need either the p/s piping, or a hydro sep

The actually have a good piping section in the manual. All the data and pics you need.

mopar440_6

hot_rod said:

The Navian manual will show the minimum flow the boiler needs. As long as all loops run, you probably have sufficient flow to not need hydraulic separation.

Are you using glycol, be sure to factor that into the pump sizing. 35- 40% should be fine, if you use a good quality, not diluted, glycol.

No plan to use glycol as all components are within the heated envelope and the building has never dipped below freezing in the last 8 years even without heating.

Below are the PQ curves and flow rate chart from the manual for the NHB series boilers. Should the pump be sized for boiler head (highest) or boiler head + emitter head (combined)? I assume it would provide additional benefit to use an ECM pump if switching to a primary only system?

hot_rod

In your drawing you have a boiler pump, use the model the manual shows.
You should not that boiler as a direct piped, single pumped system. Stay with the piping drawing you have.

For the distribution side you need the gpm and head requirement. Are the loops zoned?
If so, a delta P type ECM is a good option

mopar440_6

hot_rod said:

In your drawing you have a boiler pump, use the model the manual shows.
You should not that boiler as a direct piped, single pumped system. Stay with the piping drawing you have.

For the distribution side you need the gpm and head requirement. Are the loops zoned?
If so, a delta P type ECM is a good option

Manual specifies the UPS15-58FC.

For distribution side, single zone, 6.15 gpm and 8.5 ft. head per LoopCAD when the system was initially designed. The UPS15-42F curve fits the best but that pump may have been discontinued. UPS15-58FC is next best fit unless an ECM pump would provide better efficiency.

GroundUp

A simple fire tube such as a Lochinvar Noble is about the same price as the NHB, and could be piped direct. This would simplify everything and keep cost down as well as raise efficiency slightly. The 120* SWT will never be attained with a 20* delta in a high mass slab like this, FYI- you're looking at closer to a 90* SWT to maintain a 20* delta with a 15-58. I do several dozen of these shop/barn type systems a year using the Noble in most cases, and anything with adequate flow (like yours) gets piped direct.

Ironman

GroundUp said:

A simple fire tube such as a Lochinvar Noble is about the same price as the NHB, and could be piped direct. This would simplify everything and keep cost down as well as raise efficiency slightly. The 120* SWT will never be attained with a 20* delta in a high mass slab like this, FYI- you're looking at closer to a 90* SWT to maintain a 20* delta with a 15-58. I do several dozen of these shop/barn type systems a year using the Noble in most cases, and anything with adequate flow (like yours) gets piped direct.

And the Loch is a much better boiler.

psb75

Lochinvar Noble. Not Navien.

mopar440_6

GroundUp said:

A simple fire tube such as a Lochinvar Noble is about the same price as the NHB, and could be piped direct. This would simplify everything and keep cost down as well as raise efficiency slightly. The 120* SWT will never be attained with a 20* delta in a high mass slab like this, FYI- you're looking at closer to a 90* SWT to maintain a 20* delta with a 15-58. I do several dozen of these shop/barn type systems a year using the Noble in most cases, and anything with adequate flow (like yours) gets piped direct.

@GroundUp thanks for the real world info. I wasn't aware Loch had started making anything below the Knight series. Would a direct piped system benefit from an ECM pump (Alpha15-58) or just stick with the UPS15-58?

hot_rod

Im a lochinvar fan, I think all the brands have  entry level mod cons  now

it needs to be a fire tube to direct pipe

GroundUp

You could certainly save a few bucks on electricity if you wanted to go with an ECM circ, but at double the upfront cost of a standard 15-58. As far as performance goes, there is no benefit one way or the other for a single zone system like this IMO.