Advice needed on new hydro air install

[Giantsean]

Hi All,

I've recently contracted an HVAC co. (basically a 2-man operation, friend of good friends situation) to install a hydro-air setup in my house. Vital stats below:

1952 cape
Southern Connecticut
1st floor mix of brick on block (old side) and brick on wood (~1300 SF)
2nd floor wood framed front and rear dormers (~1150 SF)
Previously heated by Navien CH-240 and a mix of cast iron radiators + baseboard

New setup is:
Same Navien boiler
2 x AS TAM7 air handlers (1/F in basement 2 ton; 2/F in attic 2.5 ton)
1/F is 2 zone (about evenly split) - old "colder" side (brick/block) and new "warmer" side (brick on wood) - registers/returns in floor
2/F is single zone - registers/returns in ceiling
Honeywell HZ221 ZC
returns in each room except bathrooms and kitchen

So far these guys have seemed pretty good. Not the most polished or conscientious but not outwardly shady by any means. Right now the ductwork is all done and heat is on, just waiting for the cooling portion, which tie into some of my issues/questions.

First issue:
Originally the contract called for 2 ADP B series air handlers and Rheem RAPM series 14 SEER consensers (technically the quote says they are AJM but they verbally told me they'd be the RAPM - they gave me the cut sheet for those). I was quoted the variable speed fan option and when the first AH arrived and was installed, I went up to inspect and found it was a 3-speed. I called them on it and they promptly pulled it out. Can't recall how/why but we got started talking about upgrading the units but I asked whether they can upgrade to the AS TAM 7's. They told me we could for an additional $650 (I thought he said for both vs. each, but more on that later). They then suggested to upgrade the condensers to AS Silver XI units. The difference in the quote from the ADP/Rheem to all-AS was $2000. I have this in a text and in a quote softcopy.

Fast forward to now and it's time to buy the condensers. They are telling me they messed up and they'll need an additional $3500 (up $1500 to the quoted $2000) to go with the Silver XI's. They swear it was a mistake yadda yadda. I'm willing to take them at their word but I'm a trust but verify type of guy. Trouble is that it's extremely difficult to verify when there is no real pricing available for Trane/AS stuff. So my question is simple. Does the addition of those units (TAM7/SilverXI) justify a $3500 delta over the ADP/Rheem stuff? Note per them this is unit price only, no markup.

Second issue:
I was quoted 2 of the same HHC's for both of the TAM7's, which was model BAYWVBB07SCA0AA. What was actually installed was a BAYWAAA05SC1AAA for the 1/F and BAYWVBB07SC1AAA for the 2/F. From what I can tell the AA05 is good for 42K BTU and the BB07 54K BTU. Besides being annoyed that they were different, my first thought was why would they put a bigger coil upstairs for rooms that are WAY better insulated than the rooms downstairs, and has only one zone. The only thing I could think of is that with the AH in unconditioned space it would need a little extra. Still from all the "rules of thumb" I could find, 42K is a bit undersized for a 1300 terribly insulated house in Connecticut. I can't imagine the price difference is THAT substantial that it would be worth it to rip me off, so I'm kind of scratching my head at this one. The problem though is that if it gets cold enough (about 40F outside) I cannot hit 70F inside... max is about 68. Not sure if issue 2 is the reason, a contributing factor, or there are other issues (and I don't expect anyone here to know w/o more info)

Third issue:
The Navien has DHW prioritized, and I don't even know if there is an option to NOT have it like this. Problem I'm having is is that when DHW is called for, the AH's blow cold air. I understand there are ways to avoid this (shut off the fan when the call for DHW is made) but I don't know much about the options. I'd like to talk to these guys from an informed standpoint so any info would be great

Fourth issue:
Whenever the AH provides heat the ZC has the emergency heat light lit (it is all or nothing AFAIK). Not sure why this is - either this is how hydro works or it's wired funky. Not a huge deal, more of a nice to know.

Sorry for the book and I am not out to stiff any pros... I just want to be as informed as possible. I have been burned before and it is quite hard to find local people to ask that aren't trying to sell you on something.

Many thanks for any advice!

 

[Dana]

It takes a completely uninsulated 2450' house heat load as high as 42K at +40F, and you may even need keep the windows open or something to hit that number. Even a marginally insulated house that size is likely to have a heat load less than 42K @+5F (which may be below your 99% outside design temp, if you're on the coast) if it's reasonably air tight. If the house is leaky it's pretty cheap to air seal it to bring the deisng heat load down, even without adding insulation. If you have old wintertime fuel billing when the Navien was heating using the cast iron rads to heat the place with exact meter reading or fuel-fill-up dates and your ZIP code we could put some hard limits on what the real heat loads are.

For the record, I have ~2400' of 2x4 wall conditioned space with 2x6 cathedralized ceilings + 1500' of semi-conditioned insulated basement that never drops below 65F, in a location with a 99% outside of +5F, and it comes in at about 35K @ +5F. It'll be under 30K @ +5F when I'm through with the long term planned upgrades to the place.

Most air handler controls are designed to turn off if the incoming water is too low, which should take care of the priority HW problem. If it's not able to keep up with the loads at +40F outdoor temp It may be that coils are sized for 42K assuming 140F or 150F water, but it won't be anywhere near that if you're only giving it 110F water. With hydro-air you would have to tweak the outdoor reset curves on the Navien pretty radically from however they were set with the cast iron radiation. What sort of water temps are you delivering, and what water temps are the air handlers returning to the boiler?

Iron rads provide higher comfort than any air handler, and even ECM drive variable speed air handlers take more power per BTU of heating than even dumb hydronic pumps. If you haven't ripped out the rads, use 'em- even if broken into zones there is usually sufficient thermal mass to not run into short cycling issues, unless you micro-zone the hell out of the place with miniscule loads on some of those zone. Hydro-air is almost always a (sometimes large) step down in comfort and power-use efficiency from real radiation, if maybe side-step or lower step down in comfort from fin-tube baseboards.

Moving to hydro-air from radiators solves nothing, and may even increase the-as-used heat load, since the room-to-room pressure differences created by the air handlers when running induces outdoor air infiltration. If the ducts are up in the attic above the insulation it's even worse sometimes significantly worse! To minimize these effects duct design has to be perfectly balanced with separate returns for every doored off room, and the ducts need to be perfectly air-tight, sealed at every joint & seam, and every register boot needs to be air-sealed to the ceiling/wall gypsum or subfloor.

If you were installing the air handlers to be able to have air conditioning, a heat pump or straight AC unit would probably have been a cheaper and higher-comfort solution. The peak cooling loads on your house are probably ~ 20,000 BTU/hr or so (unless you have huge amount of west-facing window area), but your peak heating loads are probably over 35K (but probably under 42K) which leads to a bit of mis-match when using the same ducts & air handler for both heating & cooling. If asked ahead of time I would have recommended against hydro-air, or using any hydro-air as a second stage to the radiators, if for some reason the rads don't keep up on their own.

The "right" solutions call for a real load calculation ahead of time, but in the absence of that, a fuel-use calc for the heating load and a ton of cooling per 1200-1500' of conditioned space would ball-park it reasonably for a CT location. A fuel-use heat load calculation is measurement, using the boiler as the measuring instrument. You can't easily do that with cooling loads, but even in poorly insulated houses in Georgia the cooling load ratios are rarely over a ton per 1000' of conditioned space, though the hacks who don't run load calculation tools all use a ton per 500', "just to be sure" and that allows them to get away with leaky uninsulated ducts in the overheated attic, not that it's doing their customers any favors. Even at this late stage, it's still running the fuel use calculations to assess the heat load to figure out which way to go from here.

 

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[Giantsean]

Thanks Dana for the extremely long and detailed reply. I have learned quite a lot just from this!

I should have prefaced each subject line with "Yes I should have done a Manual J, but..." In fact I tried to get anyone who would listen to give me an actual heat loss analysis - even willing to pay for it - but I either talked to the wrong people or nobody around here thinks it's worth it. This was probably the most frustrating part of the process for me (aside from agonizing over which system was best - which I already knew... more on that below)

So if I am reading your note correctly a 42K coil by itself could head the whole house, and I have 42 down and 54 up, so in theory it should be more than enough if everything else is set up correctly. The ductwork seems reasonable enough... not the tightest possible but nothing I can't remedy with some sealing and maintenance. There is probably more flex run than pros would put in their own homes but it does not seem to be an unreasonable level. The longest run of flex is about 15' and that's just to hit a difficult spot. I am digging up my old gas bills to report those back, but for now there's enough to do to get it to work

So to my immediate problem, some interesting updates. First I found the hydro control board in the AH had the DIP switches completely NOT set at all (vs set wrong) so I fixed that per the manual. I also messed w/ the K factor setting of the Navien (if you are familiar w/ the units, if you have an OTR hooked up it limits how much you can tune it via remote or DIP switches). It was set at 4 originally (actually 6 when it was first set up) and I took it to 3. This morning when we woke up the house was 66 with stats at 70. The ZC was solid green for both zones so I'm wondering if the aquastat on the return pipe (coil to the hydro control board) kicked it off due to low temp... which would be funny because it was NOT doing that before, hence the cold blowing air. The water at K factor 4-6 ranged from 130-150. When it was supplying the rads/baseboards it was getting up to 160 but never beyond that even at K Factor 6 (I tried... they sent me a hi temp board at some point but eventually it became a moot point. Still have the board tho )

I have not checked return temps to the boiler (I forgot how actually lol but trying to relearn). Another difference from before is that the unit was moved to a new location and at the same time was replaced under warranty because it had just sprung a leak in the heat exchanger (perfect timing!). These guys installed the quick install manifold pretty much at the demand of navien (so they say... it was a $450 part!). I do not know much about that manifold - something else to learn - but I can't see it causing any problems if it's a factory made part, assuming it's installed correctly.

Finally, you are singing to the choir on forced air vs. rads. To be fair most of the house was baseboard, and cheap sh*t at that. The reason we went with central heat was that we are doing a major reno at the same time, and it solved a bunch of design issues. Since we wanted ducts for cooling anyway it seemed to make sense, and the world seems to be raving about hydro (I was never convinced and I was right). The big reason though was , that my wife wanted clean walls despite me telling her it wouldn't be as comfortable. We did ALMOST go with furnaces (either attic only or both floors) thinking they would put in more heat, but for all the negatives of furnaces we decided on hydro ("we SWEAR it gets really hot... REALLY!") In the end I am still glad that we kept a boiler for all the reasons you mentioned. I am in fact keeping the rads including my prized cast iron baseboard for installation into my man cave, where I will spend the winters in comfort while my wife enjoys her freezing wall space

Ultimately I am really impressed by the AH/Trane equipment and very happy I upgraded over the ADP stuff. As both an IT guy and a DIY type I appreciate the fact that these can be tuned, and I am really looking forward to learning more about the system. Thanks so much again for all your help!

 

[Dana]

So, you have over 95K of air handler in the house and it's not keeping up?!!

With oversized hydro-air handlers you probably DON'T want to use a K-factor curves, since it doesn't really buy you anything. The incremental marginal gains in combustion efficiency of using the curve is potentially offset by the increased power use. You can probably heat the place fine with a fixed 135-140F output temp on the Navien, which should return water in the 115-120F (tweakable with flow) to the boiler to get ~93-95% efficiency out it, and it would deliver comfortable 105-115F exit air at the registers, which is a comfortable temp at the modest air flows you should be seeing. If you lower the water temp the combustion efficiency will rise a tiny bit, but so what? The AFUE rating on the thing is 93.3%, and you'll be able to hit that with 135-140F water.

If you look at the tables on p11, you'll see that the BAYWVBB07SC1AAA delivers about 25,000 BTU/hr with 150F entering water temp at a water flow of 3gpm, and and air handler flow of 1050 cfm whereas the BAYWAAA05SC1AAA puts out about 18.5K @ 450cfm air handler flow. The combined output even at min-speed with 150F water is probably higher than the actual design heat loads of those zones. With 140F water it'll put out less heat than that at the lowest air handler speed, but at the highest speed the output is about 30% higher. With 140F EWT you'll get about 80-85% of the output that it specifies at 150F EWT, so there's no point to feeding it 120F water just to gain an other 0.3% of combustion efficiency out of the boiler. Any gains in combustion efficiency are probably being more than offset by cost of extra air hander power used for the longer run times when feeding it extra-low-temp water.

I suspect that with the rads you probably didn't actually need more than 140F output water either if you used a "set and forget" strategy with the thermostats, but to get reasonable response times using a setback strategy peaks as high a 160F was probably necessary. Just a guess...

The quick-installation manifold is for hydronic designers who don't understand how to assemble field-designed hydraulic separators out of closely spaced tees. It's arguably overpriced, but a heluva lot cheaper than letting Frick & Frack figure it out (or not) by ripping it out and re-trying multiple times, (provided they ever even figured out where the problem really was.) There's no rocket science to it, but it's astounding how many folks installing mod-cons haven't a clue about hydronic design. (Not sure if your contractors are among that lot, but wouldn't be surprised if they were, given that they didn't perform a heat load calc.)

 

[Giantsean]

Yeah I tried to test the water temp theory out last night and cranked the K-factor up to 6 which got the temps between 150-160. The air was blowing slow and warm and was able to keep 70 for much of the night, but we woke up to 66 degree house again. For what it's worth, it looks like the AH fan is not ramping to full blast, rather capping at a very slow speed. I suspect the way it's wired is fundamentally wrong, and maybe that zone controller showing emergency heat consistently has something to do with it.

I am not too worried about dialing in the water temps as the Navien allows you to get very granular with settings (provided you disable the OTR). I am not even worried about maximum efficiency just need heat! But it looks like water temp is ultimately not the problem.

FWIW, I have the cheapest possible thermometers installed. Not sure if something smarter can pull some more functionality out of those air handlers.

If still no joy after all that, I am also not positive that supply and return are correctly connected to the coil. Not sure that it makes a giant difference to the function but I am sure having the aquastat in the right place makes a significant difference. That said, I wouldn't peg these guys as THAT incompetent either.

Interesting about the manifold... so it's primary function is just to keep two disparate temperature pipes separate? I had read the sheet for it and it mentioned stuff like "optimize flow" etc but that might just be marketing BS. I'm still struggling to figure out how flow can be maintained with both supply and return being connected but I guess that's why I'm not a hydraulic engineer

Thx again!

So, you have over 95K of air handler in the house and it's not keeping up?!!

With oversized hydro-air handlers you probably DON'T want to use a K-factor curves, since it doesn't really buy you anything. The incremental marginal gains in combustion efficiency of using the curve is potentially offset by the increased power use. You can probably heat the place fine with a fixed 135-140F output temp on the Navien, which should return water in the 115-120F (tweakable with flow) to the boiler to get ~93-95% efficiency out it, and it would deliver comfortable 105-115F exit air at the registers, which is a comfortable temp at the modest air flows you should be seeing. If you lower the water temp the combustion efficiency will rise a tiny bit, but so what? The AFUE rating on the thing is 93.3%, and you'll be able to hit that with 135-140F water.

If you look at the tables on p11, you'll see that the BAYWVBB07SC1AAA delivers about 25,000 BTU/hr with 150F entering water temp at a water flow of 3gpm, and and air handler flow of 1050 cfm whereas the BAYWAAA05SC1AAA puts out about 18.5K @ 450cfm air handler flow. The combined output even at min-speed with 150F water is probably higher than the actual design heat loads of those zones. With 140F water it'll put out less heat than that at the lowest air handler speed, but at the highest speed the output is about 30% higher. With 140F EWT you'll get about 80-85% of the output that it specifies at 150F EWT, so there's no point to feeding it 120F water just to gain an other 0.3% of combustion efficiency out of the boiler. Any gains in combustion efficiency are probably being more than offset by cost of extra air hander power used for the longer run times when feeding it extra-low-temp water.

I suspect that with the rads you probably didn't actually need more than 140F output water either if you used a "set and forget" strategy with the thermostats, but to get reasonable response times using a setback strategy peaks as high a 160F was probably necessary. Just a guess...

The quick-installation manifold is for hydronic designers who don't understand how to assemble field-designed hydraulic separators out of closely spaced tees. It's arguably overpriced, but a heluva lot cheaper than letting Frick & Frack figure it out (or not) by ripping it out and re-trying multiple times, (provided they ever even figured out where the problem really was.) There's no rocket science to it, but it's astounding how many folks installing mod-cons haven't a clue about hydronic design. (Not sure if your contractors are among that lot, but wouldn't be surprised if they were, given that they didn't perform a heat load calc.)

 

[Dana]

If the air handlers never hit their full speed and it's losing ground with 160F water, you either don't have enough water flowing through the coil or there's something amiss in how the air handlers are being controlled. There is no WAY it shouldn't be able to keep up in this kind of weather!

The hydraulic separator's function is to keep radiation flows from affecting the rate of flow through the boiler too much (and conversely). The radiation flow requirements can differ from the boiler flow requirements by an order of magnitude, so when you really need to keep them from influencing one another, some sort of hydraulic separator is needed, so that the boiler loop flows are controlled by one pump, and the radiation flows by a different pump (or pumps.) In hydronic heating speak this is called "primary-secondary" piping, the primary being the boiler side loop, the secondary being the radiation side loop(s).

When you tee the loops into a VERY short section of pipe, (as in the quick-install manifold) the pressure differences imparted on that very short pipe aren't big enough for the flows to interact much. But it doesn't take much impedance (pipe length between tees) before that's no longer the case. The rule of thumb is that the tees the primary loop can be no further apart than 4 pipe diameters before it begins to be a problem. (If not the primary loop, the secondary loop- either is fine- the math works both ways.) If that's not do-able with the plumbing type used (can't get there with PEX, for instance) a fatter section of pipe or a commercially made hydraulic separator (typically more expensive than the quick-install manifold) can be used. At the radiation flows need in most residential applications that's rarely necessary- closely spaced sweat-copper tees usually works just fine.

Hydaulic separation with tees:

The Navien Quick Install manifold is just a fatter section of pipe (that tees closely on the primary loop) to get the < 4 diameters requirement well under control:

Other Hydraulic separators:

If you want to see the math we could go there, but that would really just be an unnecessary academic exercise (even for most hydronic designers.)

 

[Giantsean]

Wow thank you for that detailed explanation. That is a pinnable post in itself!

So here are some updates based on more observation and trial and error. Note I had pored through the manuals for the air handler, slide in HHC, and the HHC control board to try to tie together as much info as possible. Here is what I learned:

• First and to get this out of the way, apparently the 42K coil (BAYWAAA05) and the 2 ton TAM7 are a matched set. Ditto with the 50K BAYWABB07 and the 2.5 ton TAM7 (though there are more options). I surmised this when looking into the DIP switch settings. For example there is not a setting option for TAM7A0A24H21SC and BAYWAAA07 or BAYWACC08). So in that case it appears that the installers did the right thing despite what the contract listed.

• Now onto the DIP switches. I had earlier found the HHC was installed w/o the aquastat (found it in the bag) and with all three DIP switches set to ON. This setting is meant for an external HHC "box" which sits on top of the handler, not a slide in coil. After I installed the aquastat (called the "inlet" aquastat in the manual - more on that later) I had also set the DIP switches per the manual. After that is where the cold mornings problems started and the fan stopped blowing hard. Last night I set them back to original (all on) which brought the fan back to full blast. This solved the cold morning problem (temps last night were about the same as the night before) but obviously something else is wrong if this is the only way I could get it to blow to more than a whisper. Which brings me to:

• MORE DIP switches. So the control board on the handler itself has several options as well. I did not have time to experiment and I also didn't want to change too much at once to aid troubleshooting, but I suspect that these will also need to be correctly set to get this thing working right. The first bank just matches the unit to the "OD multiplier"/ tonnage (which is weird because I thought the tonnage was specific to the model ie TAM7a0a24 = 2 ton); unit type (HP or condenser); # of stages, and # of condensers. The second bank sets the CFM/ton for heating/cooling; cool-off delay; and torque vs. constant CFM mode which sounds interesting. I am guessing none of these are set and will/may affect how hard the fan will want to blow. I am still not sure how the AH knows when to use variable speeds or how "variable" it actually is (like high OR low vs. truly variable)

• Low voltage wiring - from the AH manual I can see no wiring specific to hydro - the only options are for "heat pump" or "cooling" so lacking a heat pump I was assuming that we need to use "cooling." I still do not know why the "em heat" light on the zone controller, even after reading the manual. The white wire connects to the E/Aux switch on the controller. At some point I need to learn what each of these colors "do"

• HHC piping. If I am correctly interpreting the flow, the circulators are attached to the supply side and the PEX running to the coil should run to the upper pipe on the coil. However, it does not. I do not know if this makes a significant difference but neither is it terribly difficult to reverse the PEX connections at the coil. What MAY make a difference is that the HHC board manual illustrates attaching the aquastat to the lower pipe, however it calls it the "inlet sensor" which is counter-intuitive and makes for some frustrating troubleshooting. I also do not know what this aquastat is meant to tell the AH aside from the obvious (how hot the water is... but why?)

I think that's just about where I am right now. I have attached some pics which I hope will help validate some of my assumptions. I still do not have a good answer to the DHW priority (cold air / no fan shutoff on DHW calls) but I suspect I will need to get the above running right before I get there... or it will sort itself out when I do.

 

[Dana]

Hydronic coils in air handlers are counter-flow heat exchangers. If the direction of the water flow is incorrect, the average delta-T from water-side to air-side is lower, which results in less heat being exchanged, thus lower heat output at the registers. Go over the equipment documentation carefully to verify that it's plumbed correctly. Some HVAC contractors will color code PEX for the supply & return lines to avoid those errors. It's common to see it all the same color too, but it takes a bit more care to spot the errors, and easier to make the error.

Have you measured the delta-T on the water from the coil supply to coil return? A difference of less than 10F would mean it's being over pumped or mis-plumbed (or both), something between 15F-25F would be pretty normal, 30F+ would indicate fairly low flow for the air-handler speed.

 

[Giantsean]

Thanks Dana. Would it be best to measure the difference with the DIP settings correct for the unit (vs full blast o' fan?) Or maybe both. Also I can measure supply and return from the Navien easily enough (from it telling me) but it might be harder to measure the actual loop... best I can do is use a temple thermometer and see if that works.

How about the DIP settings for the CFM and "multiplier"? Or are not there yet.

Saturday 7am update - woke up to 65F with calls for heat in both zones and the fan barely spinning (though it IS spinning). This is with DIPs on the hydronic board set correctly to the AH/coil models). I checked out the supply/return temps at the Navien itself (not the coil) last night and they were the same at around 150.. a couple of times the return actually came back higher but just one degree). Water is going through that coil but nothing is blowing out it's heat.

I am going to try to set every DIP I can find correctly and if that does not work, try to wire up one thermostat directly (bypassing the zone controller) and see if that makes any difference. It's GOT to be something with that fan getting communicated to.

 

[Giantsean]

Sunday update. After reviewing all five (count em five - the handler, coil, coil controller board, zone controller, and thermostat) manuals I have made some headway into the slow fan problem. By jumpering the three "W" terminals together (W1-W3), one can increase the fan speed in three steps (for the 2 ton TAM7 the min is ~250 CFM - which is what I was getting originally - and max ~800 CFM... a big difference!). So now the coil controller board DIP switches are set correctly and I have some velocity. I still have DIPs to play with on the handler board but this is a good start.

I have also played around with the zone controller to air handler wiring after noticing a blurb in the ZC manual about the DS/BK terminal. Apparently this tells a variable speed fan to spin faster or slower based on the number of zones calling for heat. I made the hookup on both ends (there is a BK terminal on the handler) and played around a bit but I didn't notice any difference with one or two zones calling for heat. Still it wasn't hurting anything so I left it connected.

For the life of me I cannot get this HZ221 zone controller to read anything but "EM HEAT" when it calls for heat, but that just may be that it's made for a heat pump and the next step up is they HZ322 which supports three zones and from the docs seems to just be simple single stage heating cooling stuff (not necessarily a heat pump). I don't know if using this unit which is made for a heat pump with a hydro and a regular AC will cause any problems, and I also don't know why they chose this controller... to be cheap or are they just not that bright?

My two other existing issues are still that the fan blows cold during calls for DHW (and now it blows REAL cold lol) and that my supply and return lines seems to be reversed on the hydronic coil (confirmed when I tested the upstairs zone which was off... from the "feel" test, circulator side is supply for sure. That is easy enough to fix so not too fussed, but wish I could figure out how to get the circulators/fans to stop upon a call for DHW. There must be a way aside from an aquastat.