1 manifold or 2?

mm27

Hi, everyone.
Hoping people that have more experience can point me invthe right direction.
Self building my own home & doing underfloor radiant with joist trak, 1450sq/ft tight house conditioned crawl & attic, typical 16” joist bays,3/4 advatech & white oak for the finished floor.
working out to be about 11 loops
& wanted some opinions about doing 1 manifold or 2. Have an 8 loop ep manifold already but i could exchange for 2 6 loop, dont really care to have more than 1 zone, would two be/work better? Keeping loops in the 280’ range including leader lines. Using 1/2 hepex & using my heat pump water heater & plate x changer for a heat source

EdTheHeaterMan

You will need to have a manifold with all the "supply" ends of the loops connected. then you will need another manifold with all the "return" ends of the loops connected. then there should be a pump connected to the manifold that will move the heated water from the source to the tubing. then the other manifold should be piped back to the inlet of the source to be reheated.

The heat source can be a boiler or a mixing valve or mixing station. This will depend on the system that is making the heat. If you need the boiler to make hot water 180° for other heating emitters or for an indirect water heater then the source for the radiant will be a mixing station or mixing valve.

More info needed to make a complete assessment.

mm27

Thanks for the reply, i understand that, i guess my question is am i goin to have too many gpm required for a single circulator on the secodary loop? dont have any other hot water needs other than the domestic, hence using the water heater & xchanger.

EdTheHeaterMan

Using a water heater for central heating (CH) is rarely a good idea. You may have the rare situation where this is a good idea. There are new ECM motor pumps that will solve your GPM problem. But before those pumps were available, I would just use the lowest cost wet rotor pump available. My choice was the Taco 007F. overkill for your needs but to get a lower flow pump was more expensive, and the fact that the Taco 007F pumps used a centrifugal impeller that can move different amounts of water based on the restriction that exists in the piping system that it is connected to. So you will not burn out any small pump on such a small system.

Also the fact that you do not need high temperature water (over 140°) for the floor heat is another good reason for using a water heater.

Just remember that the heat exchanger is separating the potable water (and the relief valve connected to it) from the CH system. That system needs a way to fill it, its own relief valve (30 PSI) and an expansion tank. (smallest one available like a Extrol #15) to make that a safe system to operate. To make it easy to operate, you might add an air separator purge station and auto fill to round out system. I drew this diagram for someone that is using a tank with an internal HX built inside the tank at the factory.



The dotted lines are the PEX lines that went to the radiant floor system he had. The diagram is a bit cumbersome because it matches the piping he already had in the basement. ...but it has all the components

hot_rod

If you have good access to both manifolds and can reduce leader lengths and Pex spaghetti, go with two manifold locations.

mm27

placing manifold in center of crawl, basically a 36'x36' area with small step out across rear wall, was doing some math on the head loss & calculated about 25' for 11 circuits at 280', that sound in ballpark? Wanting an ecm pump & they seem pricey at that head loss if what im calculating is correct?

EdTheHeaterMan

i came up with 22 on the rule of thumb. But most of that length is the actual radiator (280 feet of PEX) so the multiplier for fittings is probably overkill.

I like the Taco 0011F for that job. An ECM will cost more and the constant speed of a less expensive pump would do just fine, as long as you are not zoning off the manifold. If the entire 11 loops are always open then you do not need a pump that changes based on different loads or number of zones that are open.

hot_rod

You need to know the gpm for the loops to calculate head.
The RadPad suggests .65 gpm for 1/2” Pex so at 280’ 3.6 ft head for the loops.
11 loops at .65 per loop= 7.15 gpm. Call it 8gpm at 4’ head

Supplying the manifold with 1” Pex?

mm27

OK, i am using uponors' site & based on my manual j of 22k, at 8" on cetner spacing 3/4 deck, 3/4 oak floor i need 12btu/h/ft. At 10delta T they give a multiplier of .00162 per ft of piping @ 280 that works out to 0.4536 gpm. I have 1' & 1 1/4 available, i'm only half done roughing in the underfloor tubing so nothing set in stone yet

EdTheHeaterMan

hot_rod said:

You need to know the gpm for the loops to calculate head.
The RadPad suggests .65 gpm for 1/2” Pex so at 280’ 3.6 ft head for the loops.
11 loops at .65 per loop= 7.15 gpm. Call it 8gpm at 4’ head

Supplying the manifold with 1” Pex?

So the Taco 007F or the Little Red from B&G or the Grundfos UPS 15-58 will do the job nicely. all competitively priced

GroundUp

I'm going to stay out of the manifold discussion for now, but I am going to bring up the fact that no HPWH is going to heat that much radiant as well as DHW. If the radiant load alone is 22k, you're already behind.

mm27

I’m open to suggestions, that’s why i’m here. Unit is the rheem platinum & also has a 4500 watt element as well & if im calculating it right should work out to 21600 btu/hr the heat pump puts out 4200/hr. My true heat loss on the manual j is right around 18.5k was just adding in some cushion to be safe. My only option is electric, im not goin back to oil or propane. Only need 100 deg supply water to make the 12btu/sqft. Can get a second unit pretty cheap with the instant rebates from power company its a 1000$ rebate, the 50 gal unit cost me bout 750$ plus tax

GroundUp

I'm not intimately familiar with HPWH, but I do know that they need a warm space for the heat pump to work. So unless you have an auxiliary heat source already heating the home that the heat pump can "borrow" BTUs from to make hot water, you're not going to get anything above that 4.5kw which is just over 15,000 BTU and it's just the same as a standard electric water heater from a usage perspective- there is no gained efficiency. In which case, perhaps something like a 7 kw electric boiler for your radiant and keep the HPWH for your DHW? Or possibly due to the rebate, maybe dedicate a separate HPWH to the radiant alone (instead of the HX) and replace that element with a 5500W?

hot_rod

The issue withn a HPWH inside the building is it discharges cold air, around 45°F or so. Typically the heat that a heat pump transfers from the space comes from some other heat source in the building. Like a furnace or boiler.
Without some heat input, the heat pump has no where to grab the heat from. There is no "free" heat.

The air source heat pumps being used for hydronics are mounted outdoors, so pulling heat from the ambient air surrounding them.

Of course they are much more $$,but a 2 or 3 ton ccA2WHP is what you should be looking at.

I played around with a HPWH in my shop. The cold air discharge and the noise, besides the fact it was cooling and heating at the same time made it impractical.
I've heard stories of bring air into the HP and discharging it out, but even with that possibility I don't think it has the capacity to cover your loads.

So for an all electric option, an electric boiler, or a true A2WHP split or monobloc.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water heat pump systems.pdf

mm27

Yes i will have a ducted air 2 air inverter heat pump as well, i was planning for that in shoulder seasons & the radiant for the winter months. In zone 4 in south NJ, & it really doesn’t get too cold for too long anymore.
I looked at the air to water, but its a lil out of my reach price wise.
Guess my thought were if i’m making the min temp 110deg water & mix down if needed to 100 i should be sending 85-90 back into tank making it easier to keep up as oppossed to 45deg ground water. 

GroundUp

That's not how this works. A BTU is a BTU, whether the incoming water is 45* or 85*. The HPWH can not put any BTU into your home without first pulling those same BTUs from your home. You need something besides the HPWH to keep the space warm, so the HPWH can utilize that warm air to transfer the BTUs from the air into the water. If you wanted to stick with a HPWH for the tax benefits, at the very least one of them with a 5.5kw element would be required to meet your space heating demand- the heat pump function completely locked out. Personally, I'd forget the HPWH altogether and just go straight resistance but as stated earlier, you could maybe get away with a 7kw electric boiler for the space heating and retain the HPWH you have for domestic- whether or not the heat pump ever actually runs is open for interpretation.

EdTheHeaterMan

first rule of thermodynamics. the whole "can't be created or destroyed" thing


If you can get your system to work, then we can start on that perpetual motion machine!

I think that as long as the outdoor temperature is 70° we are good to go!

EdTheHeaterMan

hot_rod said:

The issue withn a HPWH inside the building is it discharges cold air, around 45°F or so. Typically the heat that a heat pump transfers from the space comes from some other heat source in the building. Like a furnace or boiler.
Without some heat input, the heat pump has no where to grab the heat from. There is no "free" heat.

The air source heat pumps being used for hydronics are mounted outdoors, so pulling heat from the ambient air surrounding them.

Of course they are much more $$,but a 2 or 3 ton ccA2WHP is what you should be looking at.

I played around with a HPWH in my shop. The cold air discharge and the noise, besides the fact it was cooling and heating at the same time made it impractical.
I've heard stories of bring air into the HP and discharging it out, but even with that possibility I don't think it has the capacity to cover your loads.

So for an all electric option, an electric boiler, or a true A2WHP split or monobloc.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_27_NA_Air-to-water heat pump systems.pdf

@hot_rod When my brother worked for a fuel dealer after they sold the fuel oil business, He was the salesman and they sold Generators. And we all know that heating systems can run on Oil, Natural Gas, LP Gas, or Electric. He got a customer that wanted to install one of those generators after we all experienced Hurricane Sandy. But this young lady wanted the generator that ran on electricity! How do you tell a long time oil account that does not have basic common sense that they don't make generators that run on electricity without insulting them and risking loosing a good customer. There is no free electric,