HVAC Sizing

	HVAC Sizing

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Subject

Author

Date

HVAC Sizing

walter_lee

07-11-2006

HeatMan

gofish

Noon-Air

walter_lee

daytona

udarrell

Bubba

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Posted by daytona on July 11, 2006, 10:21 pm

Different topographies determine different sizing.

> Noon-Air wrote:

>> >

>> >>

>> >>> When getting a new HVAC installed, how do you know you are getting

>> >>> the

>> >>> correct size for your home?

>> >>>

>> >>

>> >>Run a heat load on the house. There isn't a 'rule of thumb' that

>> >>works.

>> >>

>> >>There are a bunch of programs available on the internet.

>> >>

>> >

>> > Indeed. lets look at how long its taken bill gates to write a program

>> > that isnt full of bugs and doesnt crash.

>> >

>> > Ok now suppose we have a rock solid, building-code-approved load

>> > calculation program. 10 different people, inputting data

>> > independently, will arrive at 10 different 'answers'. Which one is

>> > most correct???

>> Take the highest, and lowest and trash them... the rest should be pretty

>> close.... go with the averages.

>> > OK now we have the exact btu gain/loss numbers, and now we must

>> > select pieces of equipment that most closely matches the heat

>> > gain/loss numbers, and still stay within the customers budget.....

>> For the most part this is true.... there are also a lot of financing

>> options

>> avalable.

>> > Guess what?? NOBODY makes a 29,000 btu gas furnace with a 57,295

>> > btu, 5 ton blower, which is exactly what the load calc says is

>> > needed..........so now what? Oversize the heating to obtain the

>> > desired cooling airflow??

>> This is going to to be dependant on the region, and the design

>> perameters.

>> > A tiny fact that most consumers are never made aware of is that a

>> > heating or cooling load calc is accurate at only one point in time,

>> > and that is when indoor and outdoor ambient temps are at DESIGN

>> > conditions. Any other time its either oversized or undersized.

>> There are multi-stage furnaces, and air conditioners available.

> How does HVAC size effect its energy efficiency?

> The region is Washington DC

Posted by udarrell on July 12, 2006, 10:00 am

gofish@gonefishin.net wrote:

>Walter_Lee@my-deja.com

>>>When getting a new HVAC installed, how do you know you are getting the

>>>correct size for your home?

>>>How does HVAC size effect its energy efficiency?

>>>The region is Washington DC

>>>

Oversizing will cause the system to short cycle therefore the humidity
will not be reduced enough, unless you cool to a very low temperature
and it will then feel cold and clammy. Washington DC, Wash. Natl. AP,
Winter Design 99% at 14-F; 97.7% at 17-F. Summer Design, at Wash. Natl.
AP is 91-F Dry Bulb, 74-F Wet Bulb, or around 44% relative humidity.
With that humidity level, a 13 or 14-SEER with a Scroll compressor and a
TXV refrigerant control should work okay with a fairly high airflow.

>OK now we have the exact btu gain/loss numbers, and now we must

>select pieces of equipment that most closely matches the heat

>gain/loss numbers, and still stay within the customers budget...

>Guess what? NOBODY makes a 29,000 btu gas furnace with a 57,295

>btu, 5 ton blower, which is exactly what the load calc says is

>needed... so now what? Oversize the heating to obtain the

>desired cooling airflow?

Right-on - gofish.
In your cited case; I would go with a separate air handler for the long
season for cooling. Heating would probably be a short season, therefore
you might be able to go to electrical baseboard heat or some other option.

>A tiny fact that most consumers are never made aware of is that a

>heating or cooling load calc is accurate at only one point in time,

>and that is when indoor and outdoor ambient temps are at DESIGN

>conditions. Any other time its either oversized or undersized.

Do everything possible to bring that heatload down as low as possible,
then size the equipment accordingly.
That one time investment will save initial costs and utility costs over
the life of the equipment.
- udarrell - Darrell

--
Air Conditioning's Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/air-conditioning-total-heat-enthalpy-latent-heat.html

Posted by Bubba on July 11, 2006, 9:36 pm

On 11 Jul 2006 04:27:11 -0700, walter_lee@my-deja.com wrote:

>When getting a new HVAC installed, how do you know you are getting the

>correct size for your home?

Add up the door knobs in your home (Ex. 21 knobs)
Divide that number by 7 (21/7=3)
3 = 3 tons of cooling.
"Thumbs Rule"
Bubba

Page 2 of 2 << first < 1 2

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