Posted By DickRussell on 05 Jun 2014 07:51 PM

Posted By Dana1 on 04 Jun 2014 11:07 AM

....When using heaing/cooling ducts for HRV it generally requires running the heating/cooling system air-handler at least on a duty cycled basis to guarantee sufficient mixing & ventilation air in each room, which doubles or triples the energy use of the ventilation system.

Why is that required for "sufficient mixing?" My HRV dumps into the air return of my zoned GSHP ductwork. With no zone calling for heat (most of the time), all zone control dampers are open, and the air flows to every register in the house, without the heat pump blower running at all, as far as I can tell.

Yep, I want to see the experimental results that form the basis for the statement by Dana1. (Not so interested in the thought experiment.)

Posted By Dana1 on 04 Jun 2014 11:07 AM

Posted By jonr on 04 Jun 2014 10:49 AM

Forced hot air ducting provides an ideal way to incorporate HRVs into houses, but this approach is not possible with hydronic.

According to references such as this one, combining ducts is only ideal from an initial cost standpoint and otherwise it is best to have a dedicated HRV supply and return to each room. Then it can always be correctly balanced.

+1 on that!

The cfm requirements for heating & cooling are an order of magnitude higher than that for HRVs, making heating/cooling  ducts ridiculously and sub-optimally oversized for ventilation-only.  When using heaing/cooling ducts for HRV it generally requires running the heating/cooling system air-handler at least on a duty cycled basis to guarantee sufficient mixing & ventilation air in each room, which doubles or triples the energy use of the ventilation system.

Good Golly Miss Molly Dana1 has joined the pro-line up, sweet! Did you know Woodgeek has named a year 2030 after you, something about your crystal ball and “PV Penetration” “Dana  RE Future”? So you are now 2030D1 thanks to Woodgeek.

HR-Sailorete(aka: sailawayrb)  should get a laugh out of that.

 

I see GBT dynamic duo Johnr-2030D1 has gained some laps on Forced Air-GBT Lee Dodge-DickRussel with yet another White Paper on HRV-ERVs  in the race against the best 2014 Pro HVAC winner!!

 

Just playing!

According to the dynamic duo's white paper, in theory, the recovery unit blower has a lower CFM (approx. 100 PSF) compared to FA (what 1-2xs more) so one could expect back pressure at the recovery unit. If you are feeding the FA blower (option 1) then the FA blower fan has to be on to pass recovery air, the FA blower is also a resistor to flow when it is not on. If you bypass the FA blower send(option 2) it does not have to be on, but, when it cycles from zone demand there would be more pressure at the FA blower than recovery unit in the mix, hence back-pressure and in the shared return, lower COP. 

So the paper ask the following questions,

It might be interesting to look at fixing option 1 by adding a check valve/damper in the furnace return duct to prevent the short circuit when the furnace blower is off.

HRV air flows would be dictated by the thermal needs/balance, but perhaps that is close enough. Or maybe not (see fig 5 discussion).

Posted By jonr on 06 Jun 2014 11:00 AM
It might be interesting to look at fixing option 1 by adding a check valve/damper in the furnace return duct to prevent the short circuit when the furnace blower is off.

HRV air flows would be dictated by the thermal needs/balance, but perhaps that is close enough. Or maybe not (see fig 5 discussion).

jonr- Interesting report, or summary report. The link to the full report does not appear to be operational. You mention the damper for option 1, but I think you meant option 2, if you are referring to TLP's last post above.

Such a damper is not necessary in my particular layout, which dumps the fresh air into the furnace exit, but with the HRV stale air inlet just placed at two locations in the crawl space. I checked mine yesterday with both a smoke pencil and a tissue paper, and there was no indication of flow out of the furnace return air grilles with the HRV on. Because the HRV fresh air into the furnace outlet is pointed downstream, and is coaxial with that duct, I expected an air ejector effect with air being pulled into those furnace return air flow grilles. I did not see inflow or outflow with the HRV on high or low speed settings. Hence, no damper is needed for this particular system.

Just under item 4, Performance Testing of Experimental Systems, there is the statement, "There was very little difference in ventilation effectiveness obtained using a low-speed circulation system with an ECM motor or the higher, low-speed air flow rates associated with the 'typical' furnace fan found in Canadian housing stock." I think this conclusion contradicts Dana1's assertion that the furnace fan needs to be operated along with the HRV to provide good ventilation if the HRV is interfaced with the furnace ducting.

It is usually stated that the HRV flows must be balanced with the furnace operating. For my house, the furnace only operates at full power during early morning recovery from overnight temperature set-back. I usually don't want the HRV running late evening and early morning since it tends to try to dry out the house, causing the humidifier to run more to replace the lost humidity. So for me, I like to balance it with the furnace off. The modulating furnace does run at other times, but only at very low power with low fan speeds using ECM motors.

I assume that option 1 means that the black duct is tied to the furnace return duct. If not, then imagine an alternative option where the HRV has both the supply and return connected to the furnace return duct in a closely spaced Ts configuration - no HRV ducts running outside of the furnace room. It works when the furnace is running and also with it off - with the addition of an electric damper in the furnace duct, between the HRV tie-in points (to prevent a reverse short circuit flow).

I suspect that most shared HRV/furnace duct configurations upset the HRV balance (ie, pressurize or depressurize the house) when the furnace runs or shuts off. But I see at least one HRV that is self balancing, maybe it can overcome this.

Back to HVAC

Check this graph out, depending on unit efficiency of the heat exchanger cross over you can expect the HRV to dump cold air into a combined FA system or room. At 0 F outside temps delivered indoor temp is 60 F for a 85 ASE. Best it gets is less than 70 F at 65 outside and 95 ASE but I imagine that unit cost some money. Complicates your thermostat and sensed air.



 IMO, I don't think it is a good idea to mix HRV-ERV-FA unless you are a pro that knows what they are doing. That in itself adds labor, design, cost, to the homeowner and begs the question why the FA OEM does not do it to assure proper integration.

I think it stands as a HR disadvantage since it is even more complicated or impossible. Perhaps, one could argue that these systems need to stand alone(for now anyway) so not really a disadvantage.

Posted By jonr on 06 Jun 2014 11:00 AM
It might be interesting to look at fixing option 1 by adding a check valve/damper in the furnace return duct to prevent the short circuit when the furnace blower is off.

HRV air flows would be dictated by the thermal needs/balance, but perhaps that is close enough. Or maybe not (see fig 5 discussion).

I missed this link, interesting telephone survey results...especially the last one.

The majority of occupants perceived their HRV to be beneficial. Most occupants understood the general purpose of their HRV; however, comprehension of the technical aspects required to use and maintain the HRV system properly was low, despite more than half having had the operation explained to them and most having been provided an operation manual (only 32% reported that they had read their manual). Further, few occupants understood the potential negative effects of a poorly operated or maintained HRV. Of the 77% of occupants who reported they understood their HRV systems, 55% had unbalanced systems, 60% had substandard ventilation and 55% of occupants with partially ducted or simplified systems were not aware of the need to operate the fan of the forced air heating system.

Ignorance of even the presence of (let alone the operation of) HRVs is rampant. I remember reading a blog post somewhere written by someone who had inspected a 20+ year old HRV system on a small commercial building, where a drive belt for the blower had long since given up the ghost, laying in the bottom of the cabinet. The motor had been spinning continuously for years, possibly over a decade, burning power to no good end. The building owner & maintenance folks had no clue what the thing even was, let alone whether/when it was working.

It's clearly a simpler proposition to balance the HRV and get it working right with a dedicated duct system. Even in the best of cases the more idiot-proof you make a system, the more creative the idiots become. Until active ventilation systems become ubiquitous (mandated?) the wealth of ignorance amongst installers and owner/operators alike will undercut the unit's potential.

Your example begs the question; if the HRV didn't work was it needed?

This new ERV puts out 240 CFM. That’s getting up there. It is the first ERV that allows users to set a desired indoor humidity level. According to the manufacturer, the ERV is capable of adjusting the amount of moisture that is transferred between the two air streams (the exhaust air stream and the supply air stream) to meet a desired humidity target.

I was watching a video on natural earth homes where the walls regulated humidity by the use of clay as a binder in plaster or part of mass effect. As far as I can tell, ventilation was through an upper window towards the ceiling that also vented stack effect to a glass enclosed interior room partition with a water fall in it, I guess that stayed warm from the sun greenhouse effect and was vented to atmosphere with exhaust/intake like a ERV. It was in Australia, where perhaps the climate was not cold? Has anyone seen natural ventilation methods without the mechanical gismos?

What’s going on here in the doc JR posted, a geothermal heat pump integrated to an ERV?

Posted By BadgerBoilerMN on 11 Jun 2014 07:56 AM
Your example begs the question; if the HRV didn't work was it needed?

That depends on the definition of "need" regarding indoor air quality, doesn't it?  It's strenuously argued by folks like Lstiburek that most homes don't "need" anything like ASHRAE 62.2 levels of ventilation to keep the occupants (and building materials) healthy. 

But that's not to say some level above zero for mechanical ventilation in tighter houses isn't a good idea, even if the occupants aren't chain-smoking incense burning chronic toast-burners who spray insecticide hair-spray & patchouli on a daily basis.

I don't recall if the blogger reported the air-tightness or occupancy/purpose of the building with the long-dysfunctional HRV.

"as anyone seen natural ventilation methods without the mechanical gismos? "

Solar chimneys combined with earth-tube ventilation was a popular approach for off-grid high performance homes back in the 1970s & early 1980s. It sorta works in some climates (better in dry, cooling dominated climates), not so much in others. You have to be VERY careful about managing condensation inside the earth tubes to limit mold growth in the system during humid summer weather. From a bang/buck point of view at the costs of PV in 2014 you get a lot more out of solar powered active ventilators than some of the old-school system using earth tube and enhanced stack effect. (Google the terms "solar chimney" and "earth tube", you'll get lots of hits with pictures & diagrams, some may even show the math, but most don't.)

In the 1990s and early part of this century the PassivHaus folks revived the earth-tube approach to tempering ventilation air (both with & without HRV in the path), but both the cost and risk of screwing it up is pretty high. Most PassivHaus ventilation designs since 2010 use straight-ahead HRV/ERV, sans earth tempering.

Toast burners, that's the one that gets me riled up!

I do turn my ERV up and down with the seasons and my mood. Clearly the need for air changes and no one has a control that will read my mood...yet.

It's strenuously argued by folks like Lstiburek that most homes don't "need" anything like ASHRAE 62.2 levels of ventilation to keep the occupants (and building materials) healthy. 

And then there are studies like this that find "the Standard 62.2 ventilation rates are insufficient to control formaldehyde concentrations below the eight hour and chronic OEHHA guidelines". The HRVs come close.

It can be hard to convince people that colorless, odorless, carcinogenic gases matter.

Excellent. Thank you. Jon
Obviously much depends on construction, climate, occupancy and personal habits. No one size will fit all. One of the reasons model codes dictate "minimums", which in many cases is more than enough.

Of course, there's a case to be made that regulating VOC emitting materials in construction products more tightly is probably going to be a better approach to limiting formaldehyde exposures than cranking up the ventilation rates to wind-tunnel levels. Even the base ASHRAE 62.2 rates are very drying in cold climate locations, and drive the latent cooling loads ballistic in hot humid climates.

Here is what some natural builders have done in Vermont and NE cold climate, little sun days, that build tight envelopes and toxin free, A RUMFORD Fireplace. The windows take care of ventilation in non-winter months I take it. In winter this heater has an intake flue from the corner and under the bench that tees off to the rock openings in the corner of pic 1 and pic 2 shows the opening in the fire place. Both air intakes vs interior air windows closed in winter, dual function. Pic 3 the concrete lintel supports the weight of the bricks above, it is cast with a curve in back to act as a venturi to prevent smoke back . It's a clean burn due to the mass there is a phase change from gas to cold condensation that evaporates, no smoke out the chimney, no CO. The mass effect offsets the cold air intake probable ten fold. Bench is a nice place to sit and stay warm, if there is a back draft it heats incoming air like a HRV.  Might get a little CO at light up but I don't think it is a big deal. Just my interpretation of how it works similar to a rocket mass heater, I need to do some more digging. I'm with Badger I'm not convinced an HRV-ERV is necessary, a mechanical gismo one anyway. 

Another pic....intake bench to left with CMU on it.

Anyone have any build experience with hydronic "Night Sky Radiation"  ? SW guys have modified an old ice melt-dam system somehow for metal roofs and added cooling to HR flooring with mass designs in hot climates. More HVAC

Pretty simply really the pex lines move water from hot night time floor mass to cold roof locations to radiate to the sky of lower temps via a pump and visa versa. The mass design has such low load they open doors and windows at night to load it and the HR aids in this. Would not be hard to set up a test fixture in any climate, now be a good time of year to test it out. Sounds like late eve burning the midnight oil. Take that data do some simple math to get an idea of winter. The metal roof is better at preventing ice dams, the latent heat from the floors-walls would help. I didn’t realize they make a peel and stick pv for metal roofs that eliminates the ugly bulk glass. I just wonder how long that adhesive holds up if it is thermally cycled often in cold-hot climate extremes although there is a warrantee of 25-30 years. I read there are also shingles. Anyone have any direct experience they put in a build? Between the two the roof line would be cleaned of bulk panels, might need the garage roof facing south too. All this passive solar sounds great in theory if you can orientate the roof to it, some lots even south facing have you grid locked.