Single Stage, 2-Stage, or Variable?

[kencogan]

I'm replacing my 24-year old American Standard heat pump (still runs!). I have quotes from several local HVAC companies that include single stage, 2-stage, and variable speed heat pumps. Current system is 2.5 tons, one zone. House is 1,500 sq feet, 2 floors, built in 1977.

After reading a few threads in this forum, I understand that the 2-stage and variable speed systems can have low airflow to the rooms furthest from the air handler. I'd like take advantage of the efficiencies provided by the 2-stage and variable speed systems, but I don't want to sacrifice comfort in those bedroom furthest away. A couple of questions:

1. Is there something that I should ask of the HVAC companies bidding on this work to determine if the higher efficiency systems will be effective with the duct work in the house (calculations? system airflow test?)

2. If a 2-stage or variable speed system is installed and I have airflow issues, is there anything that can be done to improve it after installation (or am I SOL at that point)?

Thanks in advance for your response.

Ken

[teddy bear]

Basement? Number of occupants? concerns about maintaining <50%RH during low cooling loads and high outdoor dew points? Fresh air ventilation during calm weather?
Multispeed a/c is complication, expensive, and difficult to setup and maintain.
Simple medium SEER a/c is most practical. Most complicated systems are not installed properly nor maintain correctly. You can see this by all the post questioning their operation.
Add a small whole house dehumidifier to a straight a/c and you will have perfect control and ideal comfort at any condition in a green grass climate. You can turn the a/c when the home is unoccupied and maintain <50%RH regardless of the cooling loads. Most homes are air tight enough to need a small amount of fresh air ventilation during calm winds and mild temps. Many states are now requiring fresh air to improve poor indoor air quality which means purging indoor pollutants and renewing oxygen. nits like the site sponsor, Ultra-Aire have this capability for a little more than a variable speed a/c.
Keep us posted.
Regards TB

[teddy bear]

http://hvac-talk.com/vbb/showthread....1#post19028151

Even better support to my comments. Most home owners do not think about this problem until it is to late. Then realize that any style a/c is unable to keep a space dry during low/no cooling loads.
Regards TB

[kencogan]

Basement? Number of occupants? concerns about maintaining <50%RH during low cooling loads and high outdoor dew points? Fresh air ventilation during calm weather?
Multispeed a/c is complication, expensive, and difficult to setup and maintain.
Simple medium SEER a/c is most practical. Most complicated systems are not installed properly nor maintain correctly. You can see this by all the post questioning their operation.
Add a small whole house dehumidifier to a straight a/c and you will have perfect control and ideal comfort at any condition in a green grass climate. You can turn the a/c when the home is unoccupied and maintain <50%RH regardless of the cooling loads. Most homes are air tight enough to need a small amount of fresh air ventilation during calm winds and mild temps. Many states are now requiring fresh air to improve poor indoor air quality which means purging indoor pollutants and renewing oxygen. nits like the site sponsor, Ultra-Aire have this capability for a little more than a variable speed a/c.
Keep us posted.
Regards TB

TB,
Thanks for your response. Sound like you're recommending single stage heat pump system with whole house humidifier. (Correct?) I have five quotes for the replacement system and only one company would quote only a single stage system. Maybe he's the only one who got it right!

Yes, there is a basement but no heat or a/c delivered. Air handler and laundry located there. Three occupants with a fourth at school (only home occasionally).

No issues with RH with the current system except when the local utility turns off the heat pump via radio control during peak demand periods. No visible mold.

Fresh air? No sure how tight this 1977 house is. Outside wall construction is foam panel + plywood sheeting + aluminum siding. I don't believe house wrap (Tyvek) was used. We did replace the windows about 10 years ago.
- Ken

[54regcab]

Multispeed a/c is complication, expensive, and difficult to setup and maintain.
Simple medium SEER a/c is most practical. Most complicated systems are not installed properly nor maintain correctly. You can see this by all the post questioning their operation.
Regards TB

Amen !!!

IMHO they don't save money on utility bills when compared to medium SEER. Both have about the same EER which is what really affects power bills.

Have you considered 2 systems, one for each floor?

[teddy bear]

TB,
Thanks for your response. Sound like you're recommending single stage heat pump system with whole house humidifier. (Correct?) I have five quotes for the replacement system and only one company would quote only a single stage system. Maybe he's the only one who got it right!

Yes, there is a basement but no heat or a/c delivered. Air handler and laundry located there. Three occupants with a fourth at school (only home occasionally).

No issues with RH with the current system except when the local utility turns off the heat pump via radio control during peak demand periods. No visible mold.

Fresh air? No sure how tight this 1977 house is. Outside wall construction is foam panel + plywood sheeting + aluminum siding. I don't believe house wrap (Tyvek) was used. We did replace the windows about 10 years ago.
- Ken

Yes, single stage with a whole house dehumidifier and maybe a humidifier. If you do not have a humidifier and the home does not get dry during winter weather, chances are that your home is tight enough to need mild weather ventilation especially during mild calm winds.
It is your health and home, I would measure the CO2 levels during calm winds to get a feel for fresh air change.
With the suggested equipment, you will have ideal humidity winter and summer with proper fresh air change during all weather conditions. All of my customers with fresh air change would never go back to living with the variable comfort levels and variable indoor air quality.\
Regards
TB

[kencogan]

Have you considered 2 systems, one for each floor?

Yes, even found a neighbor who did exactly that. They have the same floor plan as us.
Total cost for them is more than we can afford. Also, HVAC companies here will charge for two systems thereby doubling the maintenance costs.

[kencogan]

Thanks again TB. Our house gets really dry in the winter because we run a wood stove. We do need humidification in the winter.
- Ken

[kencogan]

Tightening up the house and ductwork is a good idea. There are ceiling fans and recessed lights on the second floor which probably have gaps around them. I also need to finish laying in the 2nd layer of insulation in the attic. Since I can access the ductwork in the basement, I should be able to seal the joints better with some aluminum tape. In addition, I could pay for an energy audit and see what else could be done.

[54regcab]

Compare the cost of 2 basic 80% furnace/13 SEER systems vs 1 large variable speed system.

[beenthere]

Is your system in the attic, or in the basement.