With the outdoor and indoor units mostly installed, it was time to tackle the ventilation components. The "V" part of HVAC, it's especially important in airtight buildings. Human activities generate CO2 and humidity and odors and other organic yuck at a surprisingly fast rate, and replacing that with a supply of fresh outdoor air is always needed. [Except around LA, where you only get to replace human yuck with vehicle yuck.] | |
In old buildings, overall air infiltration and leakage traditionally took care of that. In the seventies when everyone got all excited about saving energy and afterward when better materials and construction techniques led to tighter houses, many people learned about ventilation needs the hard way as they kept battling headaches and scrubbing mold off their walls. The modern approach is extra equipment to supply controlled ventilation and replace stale interior air with fresh from the outdoors, except that nobody wants to push air they just spent money heating out of the house in the dead of winter. The energy-efficient answer is to exchange air through a heat recovery ventilator [HRV] that passes the two air streams near each other, without mixing them, across an aluminum radiator core assembly that thermally tempers the incoming air using energy from or to the outbound stream. Typical transfer efficiency is between 65 and 80 percent, and some of the true counterflow-core European units that we can't get in the US yet are up around 95 percent. At the fairly low volumes needed for adequate air exchange even the lower-performace units can let a building "breathe" well but retain significant valuable heat in the process. | |
An ERV or energy-recovery ventilator that could also transfer humidity
was briefly considered, but with far less fiddly maintenance and in a
mostly-heating climate region the plain ol' HRV was the right choice.
I wasn't too worried about humid air, as long as it could get
processed, e.g. dried, as soon as it reached the main air handler
running in cooling mode.
Veni, vidi, venti The Synergy guys had originally planned on supplying an HRV to go with the overall retrofit and had specified a fairly small and simple one, but it didn't have the CFM capacity I anticipated needing at times and wasn't nearly as configurable. Since all the HVAC was going to get done well before the real retrofit started, back in the planning stages I had floated the idea of having the HVAC guy do the HRV piece too and they thought that would be fine. I didn't want to step on any toes as far as who might be subcontracting for who, but I had a pretty good concept of what I wanted and how to have it well-integrated into the rest of the new system and they let me run with that. So then my HVAC installer and I went unproductively round and round with what specific unit I should get, as he said he'd tell me what his supplier had available but never got around to it. I got on the net and went shopping, reading comparison articles and owner experiences at the forum sites, finding horror stories like the one about cheap Fasco motors burning up inside Venmar-branded units, and basically kept researching different brands and features and other peoples' experiences until I figured out what would work best. I finally settled on the Fantech VHR1405R (pdf) with the defrost-cycle feature and fancier interval-timer wall controller, and asked that the supplier just bloody order that and be done with it. With a firm decision in mind we also then knew what duct sizes were needed to adapt to it. A ventilation system design generally wants to pull air from near typical sources of "bad air" -- kitchens, bathrooms, basements. And my concept included adding the attic to that as it would also help circulate air through the entire second floor. I had a head start on some of this by intending to use the chimney path as one of the pickups, and the fact that the ventilation system itself would be in the basement. A new duct would be needed for the first floor, and I decided the easiest way would be to run a small line up the basement stairwell and punch it through the door rather than mess with trying to open up interior walls. So I had three vent collection routes in mind, all fairly easy to implement, and already had a place to mount a duct at the top of the basement door. |
At this point the installer had to actually stop and listen to me lay out my ventilation design in detail, as hitherto he had only a vague idea. I had three collection points around the house clearly in mind, one of which was the basement-stairwell hack which given the somewhat confined space definitely needed to be a 4 inch run with a small offset duct boot. I showed him what I meant right out of a Hart & Cooley catalog. The six-inch shot from the attic was okay since it was a longer run and the remaining one didn't need to be anything special other than a 4" takeoff easily extendable with generic dryer hose and I'd figure out what to do with it later. In other words, various separate stale-air inputs combining into a common feed to the HRV exhaust stream, like we'd even talked about three months ago. *Now* he understood what needed to be built. |
Meter move, and other fun
My electrician had a couple of minor horror stories about the power-company
linemen and their administrative structure, which had likely given me a
distorted view of their attitudes toward customers and other workers in
the field. So when one of the wire guys made some wisecrack seeming to
object to the notion of me photographing the work, I thought "okay, where
the F do you get off telling me what I can or can't photograph on *my
own house project*".
It actually led to a major misunderstanding, primarily on my part, about
who these guys are and what they do. Let's remember that they *are* the
ones out there in the middle of howling ice storms grabbing 13.6 kilovolts
in their hands to put fallen wires back up on the poles, and they don't
even get hazard-pay levels of compensation for it.
So where a previous version of this page had devolved into an excessively broad-brush rant about bureaucrats and unions and entitlement and the uncontrollable ubiquity of pictures on the internet, it turned out to be completely inappropriate and wrong and that I owed these fellas a huge apology for that. Unfortunately it wasn't until after several people had read the thing that I had the discussion that straightened the situation out and gave me the right perspective. Sure, it's true that some union situations have fostered a sense of elitism and have seen their share of abuses -- the auto industry comes to mind, including Toyota's prominent success and worker satisfaction as a strictly *non*-union company above the domestic ones that are. It's a fine line to tread, and everybody's got their own opinions. But with my small indie municipal power company they're not even IBEW, it turns out, and in that context their union is still serving the original intention of protecting workers' interests while they're out there helping people every day. As it happened that morning the data card on my camera was full and I didn't realize it at the time, so my attempts to sneak a shot or two from chest level didn't even succeed so the one guy who was being a little sour that morning got his wish anyway. |
My inspection of the day's work continued with another look inside the condenser unit, which they hadn't even closed up after wiring power to it. We weren't ready to fire it up yet anyway, as getting it commissioned needed the HVAC guy back with various tools first. But the new wiring inside it seemed a little sloppy, pulled really tight and lacking nice service loops or working slack, and then I happened to notice a little silvery shiny thing down in the works that I hadn't seen before. It was a small bulb connected to one of the refrigerant pipes that took me a moment to identify, and then only because of what was sitting next to it and what I thought I remembered seeing there before. "Hmm, this definitely ain't right", I thought. |
The kid who wired power into the unit had apparently knocked the stepping coil right off the expansion valve while pulling wires through right next to it. Not like it's really firmly attached, as it just clips to the right-angle pipe to the valve, so this seemed like an honest mistake he probably didn't even realize had been made. But I had observed that he was a bit more rough and cavalier with things than I would have liked, and he really should have spotted this and/or been more careful running power. It was interesting to see that the electronic expansion valves are basically built like a generic stepper motor. Compare how the inside of this coil looks to the one I had apart while studying voltage boost theory in regenerative braking. |
Naturally this would have made life pretty interesting for the HVAC guy
when he went to start up this unit, if it couldn't open its expansion
valve at all. But these new systems give pretty good diagnostics, and
probably would have produced a very specific error code like "E9" which
would guide us to the right area. Rather than go through that exercise,
though, I simply dropped the coil back onto the valve actuator after
squeezing the clip a little tighter so it might grab the pipe better.
The wiring still seemed pulled too tight, though, and made me wonder if there had been any slack left inside the disconnect box I could shift through and perhaps alleviate this situation. Opening the disconnect involved all of one screw, so I took a look ... |
The result of this chain of coincidental observations was emailing that
picture off to the head electrician, who was absolutely *ripshit* that one of
his guys managed to do this and was falling all over himself apologizing back
to me. Good thing I had discovered it before power was ever actually
applied, as there would have been some entertaining fireworks not to
mention a distinct possibility of "arc flash injury". I assured him that
nobody had to come back that afternoon and that I'd just fix the wiring
myself. Our relationship had already become both friendly and technical
enough that he trusted me to do that.
In the heat of the moment both of us figured that kid was done as an employee, but the electrician is a really nice guy and after a strong admonishment he decided to keep the kid on, just barely, under strict probation to straighten up and work more carefully. The answer to the original question was that there *wasn't* appreciable slack available in the disconnect box, so I figured I'd just run a new piece of romex later and keep its sheath intact most of the way up to the connection block. But not now, I didn't want to make extensive changes before they were completely done with this. |
That wasn't the right answer, though. The room thermistor is behind the
slots in the lower right corner and far enough below the warm spots on
the circuit board up near the display that it doesn't appreciably self-heat
after all. The right answer came later from Daikin's applications-engineering
department, a field setting that allows configuring a thermistor
offset to compensate for inaccurate reading. I plunked in "1C-A-04" to
configure a -2.7F offset and then it was in dead-nuts agreement with
everything else.
This particular system depends entirely on the controller thermistor to sense room temp, where some systems depend more on a sensor in the return-air stream to determine demand. The latter scenario would NOT have worked well for two reasons: it requires the blower to always be running, which isn't necessarily the case, and the fact that the HRV would be dumping air at a different temperature into the return would totally confuse it about the actual temp in the house. So having this one accurate was fairly important. In further playing with the controller I found that many of the data parameters supposedly available under the "maintenance menu", particularly for the outdoor unit, were simply not present. I could see how many steps the indoor expansion valve had opened, but the outdoor expansion valve kept coming up as "--" as did other things of interest like compressor RPM, fan step, and outdoor ambient temperature. After reading the lovely theory in the manuals that all of this data would be readily available, it was *profoundly* annoying to not have it. Daikin's application-engineering group couldn't come up with any better answer than "that's just the way it works" and blamed Japan for the omissions. Like with so many other product deficiencies of this sort, as soon as you cross the pond there's no recourse or remediation to be had. Hmmph. At any rate, I was pleased to discover that the blower is *whisper* quiet by comparison to the old furnace, even on high fan. With its fairly large wheel radius, it doesn't have to run very fast to move a generous amount of air -- I could barely hear it upstairs, especially through my freshly reworked registers, but there was all this *breeze* coming out of them. |
Commissioning, sorta
With system operation stopped and quiescent but still powered up,
I could hear a characteristic soft
high-pitch whine of the inverter running. It was a little mysterious
why that would be when the compressor wasn't spinning but after observing
it alternately drawing about a half-amp [with the inverter singing] and
then a quarter-amp [silent] and checking the schematic again, I realized
that it's intentional. Instead of having a separate resistive compressor
crankcase heater, a bit of current is pushed through a couple of the
motor windings in a way that doesn't cause rotation, just to dissipate
enough energy
to keep the whole hermetic assembly warm. This is especially important
in cold weather to prevent the oil from sludging and preventing smooth
startup. Downside: it's that steady warmth that attracts critters into
the box...
It was June but we weren't quite into full summer weather yet, and a cool night or two later I went to play around with heating mode. This reverses the whole refrigerant system so the indoor coil becomes the high-pressure side, and the outdoor unit would try to become "colder than cold" to draw heat from the ambient air. This is one reason older heat-pump systems would basically crap out around 40F outdoors, but with computer control and lots of sensors in key places the newer units from almost all manufacturers can still provide heat down to 0F and even lower with relatively little loss of performance. This is something that's really non-intuitive to a lot of people, who will ask "... but it's 20 degrees out, how are you getting *heat* out of that thing??" The magic of the refrigeration cycle makes it work, even handling cold weather with a COP still greater than 1 so it's still much better efficiency than straight-up resistance heating. |
Everything seemed to work great -- after a bit of standby preheating, the air-handler came on and the indoor coil got nice and toasty. Well, that's relative, as a heat pump generally produces air around 100F and none of the parts get up to really high [aka unsafe] temperatures like in a combustion appliance. I popped open the unit cover briefly to feel how uniform the coil heat was, and noticed that there was dew all over the expansion valve and the small liquid pipe going out of the unit. In fact that whole piece of the line was wet enough to start dripping down into the cabinet insulation right at the hole where the pipe goes through, and I thought this was a little odd. | |
First of all, why would the indoor expansion valve be used at all? This
was supposed to turn around and be the hot side of the whole system, with
expansion [and thus the big chill] happening once the refrigerant returned
back to the outdoors. I even asked Daikin's application-engineering group
about this and sent them the picture and they had no idea, they thought
something might be wrong.
Later I found out that in many circumstances it's actually normal behavior and gives the whole system better efficiency -- i.e. a little bit of depressurization and expansion is done indoors to extract the last little bit of useful heat from the working fluid, and neutral or even cool liquid that's already starting to get a little bit of flash-gas bubbling in it is sent to the outside instead of carrying some of the heat back out of the house. That's another reason the liquid line gets insulated in these systems, because it's *not* always going to be at a moderate temperature. I finally found an explanation in one of the Daikin service manuals, cryptically named SiUS281117 (pdf) in the typical fashion of how they present their online documentation: In heating, the indoor unit electronic expansion valve is used for "subcooling degree control".So that's exactly what I was seeing -- a little bit of cooling done where it would actually benefit what the system was trying to produce, and the rest of the expansion happening outdoors where things get *really* cold. To head off water problems stemming from this, I put a spare bit of pipe insulation around the liquid line on the inside of the cabinet and butted right up against the inside of the box. Something else that the factory should have provided, probably. |
Big holes
Next step was to foam-fill inside the cinderblock holes and around the interior space, which took on a somewhat anatomically amusing shape as the foam expanded. Yes, this got cut back later... |
Another bit of magic, or at least astounding coincidence, happened concurrent
with running this ductwork. The exhaust pipe was the longest run and would
be going out the wall, and something would have to prevent outside air from
coming back
in under wind pressure or whatever when the ventilator wasn't running.
It needed a backdraft damper, essentially a one-way check valve for
airflow, and
rather than the typical klanky metal-flap type that we often hear rattling
on a windy day I opted for a more elegant solution. I had just ordered a
Cape backdraft
from Tamtech that week and figured it wouldn't arrive for a few days and
I'd have to install it later, but it showed up *this very day* via UPS,
just in time to be worked into the project.
Literally -- The HVAC installer was just starting on the exhaust hose and
went out to his truck for something, and came back saying "were you expecting
something from UPS?" -- and there was the box with the damper sitting on
the doorstep. Next-day service, from generic "UPS ground". We worked
it right in, using its own tube as the connection from the inner core of
the flex duct into the PVC pipe.
This all happened so fast and I got a phone call in the middle of it, that I never got a picture of the damper going in before it was all fastened up and done. But a quick look at Tamtech's website link above makes it pretty obvious how the damper works. |
_H* 120702