Hello to the forum, forgive me in advance but I've got some stupid question re: cooling/air conditioning of a home. I'm interested in building a new home, hoping to achieve net zero status. We're in Lubbock Texas, so we get both ends of the weather extremes, mid 90s in the summer, low 20s in the winter with frequent deeps in the teens and single digits. We've also got another issue: my daughter has asthma/breathing problems and that makes our current forced air system a big hassle.

Because of that we're very interested in the radiant floor heating. Great, that covers the winter but I'm not quite sure how to cool the house in the summer. I'm very new at this so I don't quite understand what role the HRV plays in cooling a house---it circulates the air, but it has no affect on its heating or cooling, correct? so one would need a different system altogether in order to cool the house?

I've seen some homes in Texas and New Mexico that use geothermal to heat and cool the house; would it be possible to combine this with the radiant heating in the winter? I've also seen something like this from the Zehnder website:

http://www.zehnder.co.uk/products-and-systems/heating-and-cooling-ceiling-systems/zehnder-nestsystems-radiant-conditioning

--which if I understand correctly, uses the same radiant system to cool as well as heat. This would be wonderful as we wouldn't have to deal with the forced air issues for my daughter in the summer.

Anyway if anyone can help me out with my understanding of how a potential system could work I would be very grateful. Apologies in advance for the stupid questions.

Marc

The HRV does exactly what it says it does(recovers heat and ventilates). It pumps fresh air in and stale air out thru a heat exchanger. In the winter when you have 70F inside and 20F outside, the warm stale air leaving the house gives up some of it's heat to the 20F fresh air entering the house How much heat is transfered depends on the efficiency of the unit. This allows for a healthy air exchange without having to heat all that cold fresh air. works just the opposite in summer. An ERV does the same thing, but will also transfer moisture between the two air streams to help maintain your internal humidity level while still exchanging air.

Radiant cooling can be made to work, but it can be a little more difficult as you do not want the radiant surface such as the floor or ceiling to go below the dewpoint temperature and start to condense moisture out of the air onto the surface. Since a radiant cooling system shouldn't condense any moisture, it will do nothing to de-humidify the air so you may also need air conditioning if humidity is a problem where you are at...

So a boiler and a chiller and perhaps also an air conditioner(and the mechanicals to integrate these 3 systems)? Or A couple ductless combined units might meet your needs with less complexity...

ron has is right.

I like the ERV for all but the most humid climates, say San Diego and Miami. In dry ,hot or cold, climates the ERV makes more sense since you will be trying to retain some moisture while ventilating bathrooms, generally.

Here in Minnesota we have short, hot summers followed by cold dry winters. Regular showering and the dishwasher running daily in a tight radiant floor heated home is all most need for humidification. You must control humidity with a quality dehumidifier and a DX cooling system.

I have found that a tight house with little solar gain will not run any cooling system enough to dehumidify to 50%, more especially in the shoulder months. This makes ventilation and moisture control critical aspects of any tight house.

http://www.ultra-aire.com/

Depending upon the size of the house, mini-split ductless heat pumps would cover that temperature range. Here in SC, we've seen a high of 107, and a low of 3 F. over the past four years. Our Mitsubishi minis have handled it easily. They are certainly a lot cheaper than geothermal. The design of the house and construction materials play a big role, too. I'm guessing Lubbock has big temperature swings, which favor a shell with significant thermal mass to smooth out the spikes. Solar gain would be a major issue in the summer, so watch the orientation of the house and window locations.

Before selecting a mechanical solution you should look at passive design options (passive cooling and heating). Given you are building a new home you will never get a better chance to design a climate responsive building envelope that can almost eliminate the need for any active cooling or heating. Check out this zero emission house which I was involved with. It is located in Melbourne Australia where the temp ranges from low 30s (so not quite a cold) up to over 100 in summer. https://youtu.be/K36OA0Q_R_E

Passive design will likely be better for your daughters asthma as you can avoid mechanical ventilation for most of the year (excluding extreme periods) plus you have much lower energy costs.

This house produces 100% of its energy needs and we built it for around the same cost as a conventional house.

There are also some other home design examples at this youtube channel https://www.youtube.com/channel/UChG6kOI3I06PMIVbJbyNP_g

Looks like the OP is long gone... Nice project Gogeteco!

For asthma and allergy issues, the best thing you can do is to eliminate carpet and install a central vacuum system to exhaust the allergens outside the home. Once you eliminate carpet and have a polished concrete or tile floor, you are well postured for hydronic radiant floor heating...and hydronic radiant floor cooling if you know what you are doing. A HRV (i.e., not a ERV...which are still not ready for prime time) is the logical choice for efficient ventilation of an energy efficient building in a non-humid climate. Investing in the building envelope and taking advantage of passive solar cooling/heating aspects is always the best starting point to achieve an energy efficient building.