pnichols
Santa Cruz Mountains
Senior Member
Joined: 04/26/2005
View Profile
|
There are also new state of the art air-to-air heat pumps for home installations that are effective under 30 degrees. Some of these can have electric heat strip boost or propane boost. At low outside temperatures their computerized controls choose pure heat pump mode, or pure propane mode, or pure electric heat strip mode, or a combination of two of the three - depending upon which mode is the most energy efficient.
They're probably using variable speed rotary compressors with perhaps two stages in series to accomplish this and their efficiency rating numbers are way superior to my 30 year old Carrier's. There's no reason other than "money" that RV air-to-air roof top heat pumps couldn't be offered in scaled down versions of these very efficient home units - with either heat strip or propane boost to deal with outside temperatures below 30 degrees.
* This post was
edited 11/06/09 10:01pm by pnichols *
Phil, 2005 E450 Itasca 324V Spirit
|
T_Bone
Arizona
Senior Member
Joined: 09/20/2001
View Profile
|
Deleted by T_Bone
* This post was
edited 11/24/09 04:23pm by T_Bone *
T_Bone
02 F350, 4x6, CC, DRW, PSD, 6spd, 3:73
32ft Serria 10yr 100% Solar
Please do not trust everything you read on the internet. Use only valid engineering information from well established Companys.
Buy UNION Work UNION
It pays off in the long run !
|
javaseuf
California's Gold Coast
Senior Member
Joined: 03/30/2005
View Profile
|
"Seems heat pumps may be a bit of a scam, to me."
Funny that when someone does't understand something, they think there is a "scam".
Heat pumps in the correct enviorment and installed and operating properly, work wonderfully.
If your expectations are to heat an entire living area when it's 40 degrees out, then your expectations are too high and your understanding of the physical operation of a heat-pump is low.
Steve
2007 Springdale 291RKL
2009 F150, 5.4 ltr.
1986 Palomino Hard-Side PUP
"Nobody knows how we got to the top of the hill, but since we're on our way down, we might as well enjoy the ride". ("The Secret Of Life", James Taylor).
|
javaseuf
California's Gold Coast
Senior Member
Joined: 03/30/2005
View Profile
|
pnichols wrote:There are also new state of the art air-to-air heat pumps for home installations that are effective under 30 degrees. Some of these can have electric heat strip boost or propane boost. At low outside temperatures their computerized controls choose pure heat pump mode, or pure propane mode, or a combination of the two - depending upon which mode is the most energy efficient.
They're probably using variable speed rotary compressors with perhaps two stages in series to accomplish this and their efficiency rating numbers are way superior to my 30 year old Carrier's. There's no reason other than "money" that RV air-to-air roof top heat pumps couldn't be offered in scaled down versions of these very efficient home units - with either heat strip or propane boost to deal with outside temperatures below 30 degrees.
The efficiency of the heat-pump in these "new-systems" still have a limit at around 40 degrees. It's the addition of electric or gas auxilliary heat that then heats the air. The physical limitations of the condensor/heat-pump still apply.
The addition of auxiliiary heat isn't new and has been around for many, many years.
|
javaseuf
California's Gold Coast
Senior Member
Joined: 03/30/2005
View Profile
|
Johno02 wrote:We have had several heat pumps in Tennessee, Mid-Kentucky and Annapolis MD. Correctly installed heat pumps are very good and very efficient. Note the word CORRECTLY. Ductwork designed and installed for an AC generally is not insulated well enough, and cannot carry the volume of air required for a heat pump. As the heatpump does not heat air as hot, it requires more airflow to provide the same heat BTUs.
Well, I sell heating and air-conditioning equipment and can say that the ducting used for a heat pump installation has the same R-Value as ducting for an air-conditioner/furnace split system.
The volume of air from the air-handler is no different with a heat pump than it is for gas or electric heat.
Oh, and increased air-flow can't physically increas the BTU output of anything. Well actually, air-flow can cool air so I guess it can reduce the BTU's but certainly not increase them.
* This post was
last
edited 11/05/09 02:32pm by javaseuf *
View edit history
|
|
|
pnichols
Santa Cruz Mountains
Senior Member
Joined: 04/26/2005
View Profile
|
"The efficiency of the heat-pump in these "new-systems" still have a limit at around 40 degrees."
Well, not necessarily so any longer. As I said in other posts above, the 40 degree outside temperature heat pump efficiency limitation is becoming an old rule of thumb.
Here's what's possible in modern state-of-the-art air heat pumps:
http://www.energysavers.gov/your_home/sp........_heating_cooling/index.cfm/mytopic=12620
Especially notice the advanced technologies sections near the end of this article.
Also note that old or new technology air heat pumps do not suddenly drop off as outside temperatures get below 40 degrees - their efficiency declines in a smooth fashion. This means the electric or gas heat booster units built into air heat pumps merely have to come on more and more as the heat pump section operates at less and less efficiency.
The new advanced techonology heat pumps in cold climates may still require supplemental boost gas or electric heating sections for low outside temperature extremes, but their boost sections will not be needed as much at any given low temperature as the boost sections in older air pump systems .... hence the new heat pumps with their sophisticated decision-making controls can miminmize the cost of heating at any given time and outside temperature. In moderate outside temperatures, of course the new air heat pumps will use less electricity than earlier ones.
* This post was
last
edited 11/06/09 12:08pm by pnichols *
View edit history
|
texasrat
Las Crusas, NM USA
Full Member
Joined: 12/18/2004
View Profile
|
pnichols wrote:There are also new state of the art air-to-air heat pumps for home installations that are effective under 30 degrees. Some of these can have electric heat strip boost or propane boost. At low outside temperatures their computerized controls choose pure heat pump mode, or pure propane mode, or a combination of the two - depending upon which mode is the most energy efficient.
They're probably using variable speed rotary compressors with perhaps two stages in series to accomplish this and their efficiency rating numbers are way superior to my 30 year old Carrier's. There's no reason other than "money" that RV air-to-air roof top heat pumps couldn't be offered in scaled down versions of these very efficient home units - with either heat strip or propane boost to deal with outside temperatures below 30 degrees.
These units are called Duel Fuel Systems - that is Ngas or propane for low temp heating and heat pump for heating at (outside)temps greater than 40 degrees. For Ac they just run in AC mode. Got one a couple of years ago and it works really great. Lowered our energy bills in both the winter and summer.
Texas Rat
* This post was
edited 11/08/09 07:36pm by texasrat *
|
Bumpyroad
Virginia
Senior Member
Joined: 12/01/2005
View Profile
 Offline
|
perhaps in some parts of the country the electric/propane/NG backup heat is a "booster" but the ones I have are actually electric furnaces that completely heat the house when the temperature gets cold enough. and when on electric heat, that electric meter starts spinning like it wants to take off.
bumpy
|
pnichols
Santa Cruz Mountains
Senior Member
Joined: 04/26/2005
View Profile
|
"..but the ones I have are actually electric furnaces that completely heat the house when the temperature gets cold enough"
That's exactly the way my 30 year old Carrier HP works and why I want to replace it with a new one with a very high efficiency heat pump section -> so that an expensive electric heat boost section of the new heat pump doesn't have to run anywhere near as much at any given cold temperature.
Air conditioner/heat pump combination units for RVs could be built the same way: Very high efficiency compressor machinery supplemented with a 1500 watt boost heat coil. As an added benefit, a high efficiency compressor section in 13.5K combination RV models would make it possible to run them with the Honda 2000 inverter generator in far more situations - of course with the 1500 watt boost heat coil locked out when using the Honda so as to run just the heat pump part of the unit for heating in moderate cold temperatures.
* This post was
last
edited 11/07/09 09:38am by pnichols *
View edit history
|
david_42
Oregon
Senior Member
Joined: 04/08/2005
View Profile
Offline
|
Doesn't sound like the OP has a heatpump, but the one in my house will keep it warm down to 12F without the backup heaters kicking in. The only time the backups are on is for the defrosting cycle every couple days. Most people who don't like heat pumps are unhappy because the air is warm (85-90F), not hot. I keep the house at 62F and 85F is fine.
pnichols - I have a Rheem 2-ton and it is so efficient that when the electrician came out to wire it, he refused to believe it only required a 20 amp 240 volt circuit. He was used to them being 30-40 amps.
|
|
|
