 Posted 3/21/2008 3:43:17 PM
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I'm pretty sure this has been done to death somewhere, and I apologize for not finding it yet and needing to ask again.
I - finally - got a Sante Fe. I have ground source (Water Furnace) AC and heating in the attic of an insulated concrete/SIPs roofed house with no attic insulation. The heat pump operation works great. However, here in south central Texas, there are many days spring and fall where the only fault in the air outside is the water. Very familar story, no doubt.
I'd like to do the ductwork as cleanly and simply as possible, of course. I have the access to do a second intake/distribution network of ducts for the Sante Fe if that's what's needed, but it's very tempting to use the one that's already there with the AC return/distribution.
What do you recommend?
- Separate network, which will undoubtedly turn out to be one or two intakes and max three outputs
- glomming onto the main air handler and managing their interaction somehow?
I'm a multi-area techie and can handle as technically as you want to describe this.
Thank you for anything you can tell me.
Best regards,
R.G.
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Posted 3/22/2008 7:48:11 AM
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| Glad to here you have a Santa Fe. By ducting the dry air from the SF into the supply of the GSHP, distribution of the dry air throughout the home is assured. The SF can handle the pressure of most air handlers. As the SF sucks air from it's location, vents are necessary to allow return air to the SF. It is possible to duct a return from the open part of the home to SF return if providing a vent is difficult. As the ducts are extended, sensing the %RH with the dehumidistat on the SF is more inaccurate. Ideally, remoting the dehumidistat to the open space is recommened. Duct kits are available from the factory. Keep us posted. Ken
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Posted 3/27/2008 7:48:04 PM
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Hi, Ken, and thanks. The unit I have has the duct kit on it, so it's ready to hook up.
I should describe some more. I have a single story house, insulated concrete exterior walls and SIP roof. The attic is not insulated from the living space and is where the HVAC equipment is located. I intent to put a noise absorption pad in the attic for the SF to sit on , and site it there. I have access to all of the ducting.
What I envisioned was to put the SF intake into one of the return boxes and to put its supply into the supply plenum. But I worried about the suction on the intake and the pressure on the output stopping or reversing air flow when the main unit was operating. So I thought about using some simple control logic to disable the SF when the main unit fan was on.
That led me to wonder about dollars per pint condensed. I have ground source AC/heat pumps, and they're already pretty efficient at what they do. I didn't do the computation when the SF came up, I just bought it. I'm not sure whether I'd save money using the SF or not. I kinda think so, and I kind of think that the period when the outdoor temps are fine, but humid would be a saving, but then the payback might be really long.
I guess the questions are:
- where can I find flow vs backpressure data on the SF air mover so I can squint the flow it will do when bucked by the main air mover?
- is any damage going to result from bucking the main unit blower?
- how do I computer dollars per pint condensed for the SF and the main unit?
Best regards,
R.G.
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Posted 3/28/2008 9:20:43 AM
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RG (3/27/2008)
Hi, Ken, and thanks. The unit I have has the duct kit on it, so it's ready to hook up.
I guess the questions are:
- where can I find flow vs backpressure data on the SF air mover so I can squint the flow it will do when bucked by the main air mover?
- is any damage going to result from bucking the main unit blower?
- how do I computer dollars per pint condensed for the SF and the main unit?
Ideally, use an independent return from the open part of the home to the dehumidifier. This avoids any dry air from the dehu supply moving bachward through the HP to the dehu without drying the home. The SF handles .3"WG pressure which is less than most air handlers produce. More than .5" WG removes less moisture and stresses the SF. HP removes 2-3 pints of moisture per KW. The SF removes 4-5 pints per KW. Best to cool to your highest comfortable temperature at 50%RH. Set the SF at 50%RH and allow the both HP and SF to operate as needed. Many find +75^F comfortable at 50%RH. Roughly every degree you raise the a/c temperature decreases a/c cost 10%. With ceiling fans, 80^F, 45%RH is comfortable to many. Operating the fan on the SF continuously with the %RH preset at 50%RH and sensing vents tape sealed, eliminates the need to remote the dehumidistat to the living space. Thanks for good questions and participation in the forum. Keep us posted on your results. Ken
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Posted 4/1/2008 3:24:02 PM
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Forgot to mention - the heat pumps are geothermal, fed 68F water from wells.
How does one get to kW per pint? Is there somewhere I can read up?
Best regards,
R.G.
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Posted 4/1/2008 5:46:18 PM
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| Typically very efficient a/cs remove 3 pints per KW. Look at the latent heat (dehumidification) removal. Cooling at low relative humidity removes less moisture per KW than cooling at high relative humidity. Therefore cool to the desired temperature, than allow the dehumidifier to control the %RH. You could measure the water removed by the a/c and the dehumidifier and the amount of electricity used. During high cooling loads, the dehumidifier will not run much. During cool weather, the a/c operates little and the dehumidifier removes most of the moisture. Suggest some fresh air whenever the home is occupied. Fresh purges the indoor pollution and renews oxygen. Keep us posted. Thanks Ken
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