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Thread: Replacing HVAC with New Unit.
01-08-2013, 09:36 AM #27
Anyways the Trane would be the best system out of the 2 you narrowed it down to. The XB 14 in a 061 model has a 2 stage/step compressor in it and with the variable speed air handler you have a good system just hope that it works good since no one has ran a load on the home. At least it is 2 stage while still could be oversized? At least it will be able to stage is wired up properly.
01-08-2013, 09:58 AM #28
It's so hard to get some people to understand that a system running constantly and just barely keeping up or even falling behind slightly on the 3 or 4 hottest or coldest days of hte season for a couple hours, is a GOOD thing. I'm not sure my wife totally understood, until I downsized by almost 1/2 what was install in our upstairs and I made a believer out of her. A system that's silent, even temepratures, not drafty and controls humidity well and even cost a few $$$ less, is truely a wonderful thing.
01-08-2013, 11:25 AM #29Professional Member*
- Join Date
- Jul 2010
- South Florida
This is Miami we are talking about , from June to November 95plus its always hot im in shorts right now with 80 f outside and the competition is fierce. Im focusing on commercial accounts from now on anyway i understand all points made. Also dont get dark till 8:45 in the summer. If u lived here u would understand
01-08-2013, 11:49 AM #30Certified parts changer.
01-08-2013, 12:43 PM #31
Let us look at summer designs at Miami FL compared to Madison WI: Miami is 90 & 77-WB for a 13F drop for 56% RH, with a 111F Heat Index; Madison WI is 88 with 73-WB a 15 drop for 49% RH with a 102F Heat Index.
However, we get real high Heat Indexes: National Weather Service Weather Forecast Office, Temperatures during the July, 1995 heat wave pushed into the 100 to 105 range across South-central and Southeast Wisconsin, while muggy air with dewpoints in the upper 70s to lower 80s added to the discomfort. The combination of heat and humidity resulted in heat index values peaking in the 120 to 128-F range; probably the highest values in Wisconsin recorded history.
The duration of the heat wave and the stuffy overnight conditions amplified its affects on humans, since it became difficult to recover at night from the daytime affects of the heat.
Heat waves in Florida typically occur during periods of drought, low humidity and mostly clear skies.
In June 1985, a severe heat wave hit the state with temperatures of 106˚F in Ocala and 105˚F in Lakeland.
Another prominent heat wave struck in 2011 when Tallahassee hit an all-time record high temperature of 105 degrees on June 15.
The highest heat index temperature reported in Florida in 2010 was 124˚F in Apalachicola on July 31.
Therefore, Miami's extremes are no worse then mine in SW WI.
In my 1937 farm home I have a little Hal-Ton window unit cooling 1300-sf in as high as a 124-F Heat Index, it kept it within 78-F & around 55% RH.
Therefore, it would seem to me something is way wrong if you can only keep people comfortable at 400-sf per ton!
Got to get off power company is going to work on Transformer!
01-08-2013, 01:48 PM #32
IMO, you need to have a "Home Energy Efficiency Audit" performed & do the cost-effective things to bring the heat-gain down, so a much lower tonnage will do the job of keeping the occupants comfortable.
The duct system is probably way too small - along with the Return Air filter area, which is greatly lowering the 5-Ton's Rated tonnage capacity...
After the Retro-work is done, do the Manual J room by room heat gain calc & then size equipment & ductwork to what it says; do not fudge on what it tells you...You will NOT get, lower tonnages, along with real efficiency, by ignoring any of the critically important 'total home' factors...!
The output of equipment should always be at least ballpark checked; - there are easy ways to do it that only takes as few minutes.
01-08-2013, 03:40 PM #33
I alsoways remind peopel that the dry bulb design in most of FLorida is the same as SE Iowa, it's just hot there longer, doeesn't have a winter and it more humid almsot all the time. But hte heat waves we get can easily match the weather there.
THe logic to oversize because it's hot most of the time, would be the same logic as buying a really big BBQ grill because you grill often. The frequency of grilling is irrelvant to the size and burner capacity needed.
01-08-2013, 06:03 PM #34Professional Member*
- Join Date
- Feb 2009
- Tallahassee, FL
I know I'm beating a dead horse here but there is no magic chart to show your contractor if your ducts are ok.
I would love to see some pictures of the existing indoor unit and the filter setup.
Just for fun since the filter size is so critical describe your current setup.
01-08-2013, 08:56 PM #35Regular Guest
- Join Date
- Dec 2012
One more contractor/installer told me - for Bryant Preferred series they had to do extra work and run like 4 wires go from from Inside Unit/Thermidistat to Outside Condensor unit for the humidification / second stage. Is that true?
01-09-2013, 12:56 PM #36
The maximum main supply trunk 1000-fpm velocity, the Return is 800-fpm which calls for a maximum of 1770-CFM or a 5-Ton system operating at 350-CFM per/ton of cooling. I'd still go with a 4-Ton system...
I prefer considerably less velocity, than the above, through both Supply & Return. Maximum Return Grille (not a filter grille) velocity is 600-fpm.
The Return Duct system would have to be sized larger, I would want the filter area sized for 300-FPM initial Velocity, if/or, when using a clean cheap fiber glass filter; that means at least two large filter areas, cutting the airflow amount by half through each one.
Even if you use the extra deep pleated filters, - the more total filter area & reduced velocity through them the better. In order to determine as much as possible what you have, - a Manual D assessment is in order here...