# AC in Radiant Home



## Cache (Sep 18, 2007)

beenthere said:


> With radiant cooling. You must use another method of either cooling the air that the dew point is below what your floor/loop temp is. or, use a whole house dehumidifier to low the indoor humidity/dew point.
> 
> Radiant floor cooling. Is a good method, if you have a lot of windows allowing sun light to warm your floors.
> And or, you use off peak generation to cool the water. Generally meaning you are storing your cooling ability by making ice at night.


I live in Utah, where summer humidity is generally below 30%. That would be manageable. If I'm not mistaken Genecarp is from NYC, doing projects in the New England area. Not sure I would risk the humidity over there.


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## beenthere (Mar 5, 2009)

Cache said:


> I live in Utah, where summer humidity is generally below 30%. That would be manageable. If I'm not mistaken Genecarp is from NYC, doing projects in the New England area. Not sure I would risk the humidity over there.


Actually. Your 30%, is just as trouble some as New Englands higher humidity.

Because some contractors will forget. That at 90°F drybulb and 30%RH. The moisture will condense on any surface that has a temp lower then 55°F. Such as a radiant cooling floor.


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## Cache (Sep 18, 2007)

beenthere said:


> Actually. Your 30%, is just as trouble some as New Englands higher humidity.
> 
> Because some contractors will forget. That at 90°F drybulb and 30%RH. The moisture will condense on any surface that has a temp lower then 55°F. Such as a radiant cooling floor.


Good point


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## Cache (Sep 18, 2007)

My state an a few others are now doing $2/watt rebate on solar systems. That is even better than the $2000 credit from last year.


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## Cache (Sep 18, 2007)

Thought I would update this thread for anyone interested. I'm well on my way with my cost/benefit analysis. For my immediate client, solar is in and geothermal is out.

The solar system will be a 6.3kW roof mount system. Installed cost is $27,000. It is comprised of (30) 210W panels and micro-inverters. They will get an $8,000 fed tax credit. State credit is $2,000. And local utility is giving them a $6,000 incentive. The system then has a net cost of about $11,000.

They are anticipating 10,000kWh annual production from the system. They have an average annual use of 11-12,000kWh.

Further review of geothermal heating vs. nat gas in their circumstance resulted in an impossible payback based on current prices. Their expected gas consumption for heating is about 69 dekatherms. Nat gas right now is $7.33/DTH. 

This client had the ability to get the geo loop in really cheap, but even still the added cost was about $7K above conventional boiler method. The solar system increase to handle the geo pump was an additional $7K net cost. The additional mortgage payment was about $80, and they'd be saving just $45/month. Not cash flow positive, and out of pocket would have a 25-year payback. 

Interestingly, they opted to substitute the snow melt system in for the geothermal. We had a system designed for a class 1 system and the resulting heat loss was tolerable to them, as was the install cost and operating cost. They were looking at an added cost of about $5K for the snow melt and estimated operating cost of about $80/month Dec-Feb. Well worth it in their eyes.


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## flashheatingand (May 3, 2008)

What are they using to for the snow melt system? So what are they going to do about cooling? The solar panel thing does sound interesting. We also have a lot of summer light, so it's interesting to hear about how well solar is actually working. I hope to hear good things. 

I would love to be able to use the sun to heat the water and/or electrical use, as mentioned earlier, I went to a solar seminar, and it wasn't cost effective. But, I would love to see it come to a point where we are able to put the suns energy to more use. 

This isn't a professional idea, so don't bust the chops. 
The thought is to run water from the garden spigot and coil it on the south facing roof-line. The outlet of the hose would be teed to the inlet of the water heater. Now, you may not necessarily have the hot water in the morning, but you probably would have a nice supply during the day time and evening. During the fall/winter, you can take down the hose should you choose. 

Crazy talk? Guilty as Charged.


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## beenthere (Mar 5, 2009)

Just build your own solar panel(not out of garden hose). And leave it up summer and winter.


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## Cache (Sep 18, 2007)

flashheatingand said:


> What are they using to for the snow melt system? So what are they going to do about cooling? The solar panel thing does sound interesting. We also have a lot of summer light, so it's interesting to hear about how well solar is actually working. I hope to hear good things.
> 
> I would love to be able to use the sun to heat the water and/or electrical use, as mentioned earlier, I went to a solar seminar, and it wasn't cost effective. But, I would love to see it come to a point where we are able to put the suns energy to more use.
> 
> ...


Yeah, interestingly enough, there are a lot of solar suppliers who haven't yet realized how cost effective this can be for new construction. Even the company that I have ties to, they are so focused on trying to get big commercial jobs that new residential doesn't get any attention. IMO, new construction residential is the most feasible way to do solar right now. 

Cooling is going to be handled by a conventional A/C duct system in the attic. It is a rambler with full basement, so only needs A/C on top level. They only have about 20,000btu sensible heat gain according to HVAC-Calc. Latent heat gain is a non issue here in the desert. We explored the idea of doing high velocity A/C, but it just carries a really high cost, and operating costs are also higher. They say that the operating costs are reduced by setting the t-stat a few degrees lower because it does a better job of de-humidification, but since that is a non-issue here, there is no benefit.

The snow melt will be accomplished by upgrading the mod/con boiler. The Class I system will only need 160,000BTUH to work under 98% of snow melt situations here. That is assuming a 30* delta T instead of the 20* that is applicable for the house. 5/8" radiant PEX spaced @ 9". They are looking at 400-500ft runs. They had intended to install a 45K-90Kbtu boiler, but will instead be upgrading to a 65K-230K. Jury is still out on the brand, but it is between the NTI Trinity Ti and the Weil-McLain Ultra series 3. Radiant floors will likely be wet method install, so the operating temp will be closer to 120*. At that temp, both boilers claim about 98% efficiency. 

As far as solar water heating, you should know that there are plans all over the internet on making your own solar heating panel and the results are pretty good. We have nat gas here, so it really isn't worth effort.


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## flashheatingand (May 3, 2008)

I don't intend to "hijack" this thread in regards to the solar water heating. It's just that my idea was keeping things simple. Building boxes requires time and a significant investment, whereas a coiled hose is simple and quick. I would think it would be effective as well. The whole thing about being "green" is that it needs to be cost effective, effective, and relatively simple.

As for the cooling thing, I would say that if you are going to take the time to install a duct system for the a/c, one might as well install a heat pump with an electric air handler. It would only cost about $500 extra and well worthwhile.


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## beenthere (Mar 5, 2009)

On your solar water idea.

Using clear vinyl hose(painted black), would increase heat transfer rate.

Garden hose has re enforcement threads/fibers in it. that reduce the transfer rate a fair amount.


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## Cache (Sep 18, 2007)

flashheatingand said:


> I don't intend to "hijack" this thread in regards to the solar water heating. It's just that my idea was keeping things simple. Building boxes requires time and a significant investment, whereas a coiled hose is simple and quick. I would think it would be effective as well. The whole thing about being "green" is that it needs to be cost effective, effective, and relatively simple.
> 
> As for the cooling thing, I would say that if you are going to take the time to install a duct system for the a/c, one might as well install a heat pump with an electric air handler. It would only cost about $500 extra and well worthwhile.


Yeah, I've thought about the addition of a heat pump many times. The issue is that the ducts would only be run to the top floor. And the electric heat would only be utilized for about 3-4 weeks of the year. Those willing to pay for radiant floors are doing so because they really don't like forced air heating. I completely agree with them. It is much less comfortable. 

Most of my clients have access to really cheap nat gas. Even a heat pump with a 4 COP like the geothermals costs more to run than a 95% efficency nat gas boiler/furnace at current nat gas prices. So the only use for a heat pump would be the couple weeks during early november and late march when it is 30* at night and 65* during the day.


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