HRV is not for heating but for ventilating,.

Just in: this report on minisplit talk at the NESEA conference:

http://www.greenbuildingadvisor.com/blogs/dept/building-science/new-englanders-love-heat-pumps?utm_source=email&utm_medium=eletter&utm_content=gba_eletter&utm_campaign=green-building-advisor-eletter

HRV is not for heating but for ventilating,.

I understand that, but I'm of a mind to try some in which the HRV helps move the conditioned air from a smaller number of sources. An example would be teaming up HRV supply ducts with minisplits in bedrooms. The natural flow created would move the conditioned air out of the bedrooms into the hallways and toward the bathrooms and kitchens where the exhaust vents are located.

works in Passive House buildings

You will see integration of IAQ products with heating, cooling, exhaust and humidity control. You will have ducts, see Zehnder as suggested.

HRV is for ventilation with both sensible and latent heat recovery.

High velocity is a HVAC term reserved for "small duct" HVAC systems such as SpacePak and Unico. We use them in the our renovation business regularly.

An integrated air "conditioning" system for "large homes" will be ducted regardless of how "tight" or "super-insulated" it may be. Yes we know how to cut the bottom off doors, my dad and I did it when replacing coal burning gravity and propane floor furnaces with "low velocity" forced air furnaces featuring a central or singe return.

We learned it for the manufactured home industry where return air regularly is run under the doors. Seems crude for a "state of the art" passive house, but if the protocol for GREEN is short doors I guess we will have to cut them all off!

It's not so much cutting doors off as not trying to get a tight fit. There is no need to run to extremes in order to try and prove something. When your systems move air at 1200 or 2000 cfm, you may have to cut doors off, but at 190 cfm, it's just a matter of making sure things aren't simply too tight.

All my R/Os had additional space on the vertical. Recently had the trim installers obsessing over eighths of an inch at the bottom. I told them don't worry about it. The door doesn't have to be right down on the deck.

Posted By sailawayrb on 12 Mar 2014 05:27 PM


Right ICF, there is no reason to experience passive solar overheating heating these days and we covered that topic quite well already:

Integrated PS and HR Discussion

I think code minimum done properly wouldn’t even be considered well insulated, much less super-insulated. I think super-insulated is likely a term more appropriate/suitable for describing Passive House, etc.

This is a good read, everyone should read this, what I been trying to explain but cannot put into words like this. I feel like I just got out of college decades ago and forgot everything I could never explain well but, still know intuitively by theory and practical experience now.

IMHO Sailawayrb (aka Sailor) did an awesome job explaining but lacks posted data, ICFH system reults and questioning aerodynamics/fluid dynamics.
Sailor seems to elude to solar/HR mass radiation/convection controlling air flow in building’s? If so, agree in part indirectly, I too question that since air will flow from hot to cold finds an equilibrium the vehicle for which in a home can be complex thermodynamics…..not that complex if the vehicle is a stairwell leading upstairs which I agree is not good design practice.

The smart “controller” Sailor has, I did not see had pressure sensor inputs other than envelope loss CFM or ACH from a blower door test? Natural infiltration, exfiltration’s for some induced design gaps in the envelope? Concrete 85% absorptivity at what inertia rate or lag time? I would think we would want to intake/exhaust in a 12 hour delay for solar. I see a lot of 6 hour daily delays, and 4-5 days to fully load/unload. How accurate is this rule of thumb and where did it come from? I like to see some test results….

Storage = Specific Heat X Density X thickness

Q=CpmΔt
where Cp is the specific heat value, m is the mass of the object, and Δt is the change in temperature in Kelvin.

I’d like to see some test results validating this 85% rate being assumed that perhaps produced some design code/material allowable including other mass material thermal properties? Looks like there are thermocouples on the water system to concrete interface? Other areas? A drawing of locations you install on a typical installation would help? Schematic of controller feed and outputs? Power draws? Been nice to see some sensor graphs your controller puts out? IE: Burner on and off vs time of day?

Most of the testing I have done of this sort includes thermocouples & pressure sensors of sorts, placed everywhere in the system we predetermine are value engineered test points that lead to conclusive comprehensive data. Isolating fluid/ concrete temps w/o an array of air pressure/moisture sensors can be misleading. We also run the same test in blocks in this case different daily, seasonal, annual temp and pressure swings at different climates zones, etc, then put the prototype product in service at different locations in the world to see if it performs as we designed it. If not back to the testing/drawing board.
Be interesting an embedded system with inner effective mass floor/walls, roofs from a renewable source to net zero off grid power consumptions.

Integrating HVAC, mass, solar, passive, HR, HRV, ducts, forced air, miniplits, etc, can be done with the proper R&D, testing and instrumentation, prototyping, production release and sustaining design changes as req’d. Probably need better than WEL collector and a lot more test samples.

No Badger, HRVs only operate on sensible heat. ERVs operate on both sensible and latent heat. Likely just a typo, but definitely not a mistake that you want to make in actual practice.

Thanks TLP. Yes, we have evolved beyond simple/crude boiler reset control. Having an intelligent controller becomes more important when you integrate PS and HR heating systems and you also want to avoid having to move air in order to maintain temp control. Some folks don’t like to have moving air in their homes and this is one reason why they often choose PS or HR heating in the first place. Here’s the controller hardware we use:

AB (RA) Micro800

We are also evolving beyond Net Zero. We are fortunate to design/build where plentiful renewable energy resources makes Net Positive relatively easy. We also believe that our future state will eventually evolve to a distributed power system approach using Net Positive buildings using only renewable energy resources. This approach would provide a more robust power system and better address the challenges of a growing world population currently using expensive/dwindling non-renewable energy resources that are likely altering our world climate. Of course, this ultimate green building future is a long way off and far from assured as we may well become extinct long before this ever has a chance to happen.

"HRV and ERV systems all require ducts and vents .... either way your going to be running Ducts in your home...." Ricky: Good point. I suppose the choice is running the duct for ventilation OR duct for conditioning. Seems like unducted mini-splits and ducted HRV is the way to go, if for no other reason than the use of smaller flexible ducts. But, in cold climates the intake air will need to be heated, so now an inline hair dryer is needed. Are these HRV intended to run 24/7, or can the house hybernate while I'm away in the winter?

the HR in HRV is for "heat recovery". These units are designed to pick up heat from the outgoing air and heat up the incoming air; that's how they can be used in cold climates without integral heating. The efficiency of the units are listed on their specs and vary from 75% to 95% (roughly). The more efficient are more expensive as you would imagine.

You can turn them off when you are away, but you and the house are better off leaving them on continually IMO.

Correct, the HR in HRV is for Heat Recovery. The ER in ERV is for Energy Recovery…although it likely should stand for Enthalpy Recovery…

Since ERVs transfer both temp (sensible heat energy) and humidity (latent heat energy), they are total enthalpic devices. This total enthalpic energy transfer is typically accomplished using a rotary air-air enthalpy wheel.

Enthalpy Wheel

HRVs only transfer temp (sensible heat energy), which is typically accomplished using a simple air-air heat exchanger.

I will just point out here, for the casual reader, that in some extremely cold climates, HRV and ERV units do need an intake heater to prevent the media "wheel" from freezing up. I have an Ultimate Air Recoupaerator and that happens at about 12F. When it is in danger of freezing up, it either shuts down or turns on an optional preheater, if so equipped.

Enthalpy would apply if pressure were constant, but in the case of a home in taking and exhausting air that is not the case. When heat or cold air enters a room via windows/doors/HRV/ERV there is volume, gas, temperature, pressure exchanges to a constant value equilibrium state let’s assume. BTW: Pressure flows from high to low, in a vessel such as ducts pressure can generate heat at the boundary layer, same as walls, floors, wheels, restrictions (carpet at the bottom of a door creates boundary turbulence, not efficient) Laminar flow is at center. Pressure can also change based on velocity (IE: venturi effect, convergent, divergent ducts) To complicate matters, the envelope or room container(s) if you will may not be completely sealed or pressurized. Each room, leaky ducts, etc, can have different gas models to transfer heat or create work, a gas constant can be assumed. You can use P*V = M*R*T, P=final pressure, V = volume of the system when in equilibrium (ducks, plenums exhausted and at rest, blower off) , R=universal gas constant, t = final temp….to get a feel for this. Look at the Enthalpy formulas, I could not find one that applies to these parameters?

I think I'm going to handle the fresh air with two RenewAire model EV90P units.

One HRV unit with one exhaust in the main level bath with fresh air to living space.

Ditto with the lower level.

They have a controller that runs an adjustable amount of time each hour. That should keep things fresh while away for a few months.

Two mini-splits main level only.

That's final, until I change my mind!

Thanks to all for the dialogue, most helpful!

Posted By Boyne on 14 Mar 2014 04:25 PM
I think I'm going to handle the fresh air with two RenewAire model EV90P units.

One HRV unit with one exhaust in the main level bath with fresh air to living space.

Ditto with the lower level.

They have a controller that runs an adjustable amount of time each hour. That should keep things fresh while away for a few months.

Two mini-splits main level only.

That's final, until I change my mind!

Thanks to all for the dialogue, most helpful!

Did you figure out how how to keep the rustic look? I know we got a little tech out here, sorry! I'm going after natural earth building w/ natural wood accents will have the same dilemma. Only thing I can think is carve a cavity in the wood, paint some other color or flush mount.

Rustic look? I'll have some space above the master bath to hide the units and a short duct run to both the living space and master bedroom. So, looks like ducted units. I'll leave the final resting place up to the architect. Reclaimed antique oak floor, a little stone, wood paneling and maybe a live edge wood counter top if the wife let's me have my way! Oh....and a real fireplace.....zero clearance and SEALED of course!

Boyne sounds awesome good luck with that but got to say blending art s/b last of your worries you need a better design and a Architect Engineer (or have him/her come out here explain your design) because you have no response to the tech content, that knows that they are doing. Sailor, ICF is trying to get you to realize what happens to gas variables and pressures, not that he understands them any better than you do based on his/your lack of data.

Posted By Boyne on 14 Mar 2014 04:25 PM
I think I'm going to handle the fresh air with two RenewAire model EV90P units.

One HRV unit with one exhaust in the main level bath with fresh air to living space.

Ditto with the lower level.

They have a controller that runs an adjustable amount of time each hour. That should keep things fresh while away for a few months.

Two mini-splits main level only.

That's final, until I change my mind!

Thanks to all for the dialogue, most helpful!

Excellent choice. How you came to it without understanding the finer points of thermodynamics and fluid dynamics is beyond imagination! You will be happy to know that the RenewAire does not, in fact, require any sort of "heater"; mine worked fine to -20°F. And, if installed according to the manufacturers' instructions, does not need to be balanced from the unit to the exterior terminals. Magic I guess...

TLP, I am NOT seeing where ICF is discussing gas variables and pressures? There isn't any lack of data or anything new to understand or discuss here as psychrometrics has been quite well understood and successfully applied for over a hundred years. We even have DIY psychrometrics software on our website if you want to see the correlation of temps (dry, wet and dew), humidity, pressure, specific volume, density and enthalpy:

Borst Psychrometrics Software

It is not just the low temp that determines if a HRV or ERV heater will require supplemental heating to avoid freezing up. It is the combination of intake/exhaust temps and relative humidity’s that determines this. If you don’t have any moisture (humidity) in the air, there isn't anything to freeze up. It is certainly true that many HVAC pros are clueless about psychrometrics and manage to stay out of too much trouble.

Sailor. ICF raised some good questions that never got answered related to pressure flow and air/gas models several times in the thread you referenced here: http://www.greenbuildingtalk.com/Fo...fault.aspx

Posted By ICFHybrid on 15 Dec 2013 09:22 AM

The only way that irradiance (solar radiant heat) will cause air to get warm is by first striking a solid surface, causing this solid surface to get warmer than the room temp, which will then allow this solid surface to transmit heat into the room via both radiation and convection. It is convection that causes air to get warm. This is why air gets colder as you move further away from the surface of the earth

OMG.  What a trainwreck.
 
What happens when you compress a gas?

 As I said you did an excellent job explaining the issues with moving air from an HRV/ERV/FA/HR and how mass, solar radiation & convection, etc, occurs. Your controller and phase lead/lag brilliant! Nice way to capture parameters, which from what I can tell, you have mainly thermocouple inputs, no pressure or CO2 gas sensors. Are the calculators on your site and 'controller' for these applications derived from formula algorithms or from real home test data in climate zones across the US? A lot of this technology is new (passive, 2012, mass quantified, net zero, ventilation rates) and trends to obtain it. I’ve read some limited reports from home owners (nothing professional) experiences of hot and cold spots, minisplits w/ doors open/closed, wish they had put in more air handles, etc, but no real testing to develop a standard design guide.

 How are you determining your ventilation rate? ASHRAE 62.2-2013? By blower door test ACH or CFM at the leak, infiltration credit for new and/or existing homes? CO2 sensors? By climate zones or one-size-fits all? Relative Humidity? Dew point” Other indoor components? Are you using intermittent ventilation? Separating the garage or other adjacent spaces? Considering local ventilation? Rate per square feet? What about different balances and distribution types of air? Are you knocking the rate down if the home is balance, distributed (all rooms) air well mixed with ventilation?  Exhaust only? Supply only? Expensive balanced? How about a system efficiency credit or knock down? Fan flow rate? Filter spec and testing compliance? Outdoor intake location? What duck layout, duck insulation r-value? Exhaust depressurization make-up? Home owner controlled? What standard rate do you apply for a HR air transfer system you described and endorse and how is it determined?

 If a requirements definition of IAQ is “air toward which a substantial majority of occupants would have no dissatisfaction with respect to odor and sensory irritation”. There are other less expensive methods to meet design requirements. I’m not convinced ‘IAQ” requires the use of expensive mechanical equipment and super tight homes in all cases either.

 As far as I know the industry lacks data here but, if anyone can point me to it be great? I’m not looking for big words and/or polished writing skills, I’m looking for tested homes that are validated to a model or standard development. It would be nice if empirical data was made available to the public so we could all have good IAQ as we build tighter energy efficient homes.

 I’ll spend the money and design an IAQ test plan as part of my production home prototype spec development process, hopefully only two test homes, to include CFM measurements. I’ll design my build plan with installation provisions that allow for the ventilation design once the home is built and data (blower door, sensors) are available, so I can see where I am at. That way if I don’t get IAQ and net zero I’ll have some field data to look at my process to determine why.

RenewAire model EV90P claims it has core provisions to prevent freezing, can someone tell me how? And explain-proove by test or field data the rest of thier 'quality assurance" claims on their data sheet? OP would you mind sharing your system design and how you determine the above?

You will be happy to know that the RenewAire does not, in fact, require any sort of "heater"; mine worked fine to -20°F. And, if installed according to the manufacturers' instructions, does not need to be balanced from the unit to the exterior terminals. Magic I guess...

Well, actually, physics being what they are, going outside the operating parameters of any unit might require some optional work. The published specs for your unit are that no heater is required down to -10F and 40% interior humidity. Maybe you were lucky at -20F. Most companies offer optional heating units both for input air, to prevent freeze-up in certain climates and for "tempering" the outgoing air.

We chose our UltimateAir model based on efficiency, which is well over 90% compared to 63% for yours. Since we rarely go down below 12F, here, it was a good fit. There was also the question of capacity. We needed up to 190 cfm while your specific model can do only 90 cfm and we wanted a low draw unit because the ventilator is run on power from the solar panels.