OK, should have been more specific. Some systems with small evaporators and low air flow (think auto AC) cool a space by supplying a small volume of very cold air. This is not efficient, as it absorbs heat at a much lower temperature than the cooled space is actually at.
For the specific heating situation, then a larger evaporator and ample airflow will be more efficient than the situation with a small evap and less air flow, again, you want the saturation temp of the evaporator to be as close to the air temp there as you can.
That's what I was TRYING to say. In other words, transferring heat with the minimum temperature difference between hot and cold would normally be the most efficient system, especially if the whole system is designed to operate at those temperatures.
OK, this requires the suction side of the compressor to be at the evaporator pressure for the freezer, much lower than the refrigerator. There must be some kind of proportioning system like solenoid valves or maybe proportioning valves to regulate refrigerant to the refrigerator evaporator, or it would get too cold, or raise suction pressure so the freezer box won't get cold enough.
Anyway, not a very efficient system, but maybe better than having two whole systems.
The coast guard ship multi system would have almost the same back (suction) pressure if the refrigerator box had a freezer compartment in it, even if they did not it would still be quite similar, IE say 10 PSI for R22 for the freezer, and depending on the type and size of the coil in the refrigeration box it could be up to say 20 PSI.
This is quite different when you put an air conditioning system in the same system where the suction pressure could go up to 70 or 80 PSI depending of course on the entering air and the size of the evaporator. Even if you run the A/C refrigerant temperature down to around freezing say around 57 PSI there is still too bigger difference between the two systems. You could of course put a huge compressor in and use back pressure valves but that would be quite expensive to install and run.
When the air conditioning was turned on the and calling for cooling the rest of the system would get no cooling. On a hot day the A/C would want to be cooling all the time.
It is not a system I would install.
I am surprised that they allow water to be used like that.
Carrier used to make a couple of real nice evaporative condensers, I used them on many occasions.
I think they were models 9B2 and 9B3 and they handled around 6 ton and 10 ton from memory. They had twin centrifugal scroll fans and a head pressure controlled water valve, which discharged water into the bottom of the fan scrolls.
The fans threw the water onto the copper condensing coils, the excess water draining back into the scrolls, so it was not a 100% loss system, as the water valve only opened when the fans were short of water. There were no water pumps in the system, the fans did all the work.
The water boards frowned on them as they thought they used too much water. They are no longer made.
I used these in Sydney where the design conditions were 90 DB 73 WB, up here in the tropics the wet bulb is too high for them to work well.
We still have cooling towers around here for larger installations. One I did a lot of work on was a bowling alley that had two open drive Carrier
5H60 compressors and a cooling tower. I was always replacing bearings, shafts and motors on the darn thing because it dated back to the late 1950's or early 1960's. Of course the hospital complexes in the area all use cooling towers and chilled water. The university hospital is about to build their own steam plant because the power company which once had many steam customers downtown is closing their plant soon because most downtown buildings don't use steam heat anymore. The South Side of town has been taken over by the university hospital system, numerous research facilities and a number of other hospitals. There are chilled water and steam distribution complexes everywhere to service the large buildings. I suppose the new university steam plant will become the supplier for the hospital monster that ate South Side. The economy of the city shifted from steel production to hospitals, medical and scientific research.
Basically it is an air conditioning system located in the tropics in a home servicing 3 rooms, a computer room and 2 bed rooms
From a domestic point of view there is a fairly high indoor load in one bedroom (a 50 inch Plasma TV set, a hi Fi surround system and computer etc) and the computer room with quite a bit of stuff in it. The second bedroom is not that often used but also has some electrical load, a 30 inch TV, hi fi surround system and 2 computers.
As it is located in the topics the heating side is not the primary concern, but the cooling is the main use.
Design conditions are here 35 c DB 27 WB. (95 DB 80 WB) inside conditions around 25 c (77 f summer) 24 c (75 f winter) Actually I get a bit heavy handed with my design and use slightly higher numbers to ensure a good result. I have never had a client complain the system works too well :-)
It is a 2.5 ton system with a larger than required condenser to ensure the head pressure is kept fairly low. The system is on R22 and has a discharge pressure electronic speed control on the two outdoor fans to keep the head pressure low, around 190-240 PSI. The fan control is set for 200 PSI. The higher head pressure will only be there on quite hot days.
Highest recorded temperature in the city by the ocean was 40 c (104 f) but as I am on the outskirts of town inland it gets a bit warmer. I have seen it up to 40 c (104 f) once, that was not when the 40 c high was in the city, that was many years ago.
The rooms are individually controlled by 3 thermostats that each can turn on cooling or heating, but only heating or cooling can run at any one time.
The thermostat also opens a damper allowing air into the room in use. So there can be one, two or three rooms drawing air when required.
Usually during the day the computer room is used by one or two persons, sometime one bedroom is also in use during the day but the system should allow all 3 rooms to be cooled, but on a maximum day some loss of conditions can occur if all 3 rooms are calling for cooling, but that would be a rare occurrence.
The indoor and outdoor coils are fed by TX valves and there is a extra R22 in the receiver if it is required.
There are electric elements in the duct and can be used if required to help with the conditions if the humidistat calls in cooling overriding the thermostats, but they are not set up for normal heating but can be switched in if the reverse cycle fails. The humidistat is set fairly high to reduce running costs.
The humidistat is only in one bedroom, as the internal load in the computer room should ensure that the cooling runs long enough to reduce the humidity
I may fit a humidifier later, time will tell on that.
----------------------
Heating is mainly going to be used in one bedroom, sometimes the second bedroom but not often, and rarely in the computer room, although all three could be called into operation if required at one time.
Seeing the system can only have one room getting air into it when running on heating the air over the indoor coil shall be reduced, hence I will control the head pressure by controlling the outdoor fans should it get too high. Hence the question about the best head pressure.
The fact there are reasonably high indoor loads in two rooms Plus some indoor load in the second bedroom if it is in use coupled with the fact that heating is not often requite many days in this area means that the heating is a secondary consideration.
A few early mornings a year get down to 11 c (52 f) in the last 9 years twice I have seen it drop early morning to 9 c (48 f). During the day it usually gets up around 27 c (80 f) so homes do not get freezing cold as they would in the snow country.
Now getting back to heating.
In theory the correct amount of heat to keep the correct temperature would be the same as the heat loss once the room is at design temperature.
This meaning you would have the plant heating all the time. Now a hot and cold deck could do this but I cannot see what that would be a practical solution here.
Then we come to a reverse cycle system so in this case with one room requiting heating if we keep it working at maximum efficiency then we would get quick short hot burst of air to get the room up to temperature, with a certain amount of over shoot with the very hot air in the duct.
Hence I was looking for a reasonable amount of heat at a reasonable cost and keeping the room at a fairly constant temperature with a reasonable time heating system running.
I intend to put a couple of pressure switched in to turn on the other rooms when the system is heating should the head pressure get too high with only one room actually turned on. There will be a couple of other pressure switches to override the thermostats if the suction pressure gets too low on cooling turning on other rooms to bring it up.
I have also a 3 speed fan motor on the supply air which I can automatically switch if required.
I am a firm believer that air conditioning should not be felt or heard, so the system should be quiet, no drafts felt and the correct temperature being held within the design conditions.
Hence I use fairly large internally insulated ducts as the main ducts to ensure quiet running with correct size outlets.
Here on this system the 6 ton is operational, the 2.5 ton has the ductwork in and that is operational, the condensing unit is on my work bench requiring me to pipe it up and some of the house pipework is completed.
No have never done cheap house installs, mine have been superior ones by people who wanted a good job done and were prepared to pay for them and mainly did commercial and industrial stuff.
======================
While on heating I have a 6 ton system but I am using electric elements to heat this area, as it will not be needing heating very often, so running economy is not a problem.
Besides that as the 6 ton system was originally designs to have 2 fan coil units I do not like the idea of using it on reverse cycle.
The control is by a Barber Colman time proportional thermostat. They turn on the elements for a short time when only a small amount of heat us required then switch them off again, the element does not have time to get to full heat, just warming the air.
After a time it switched back on again and the element has not fully cooled down, so the air is still being warmed as it switched back on. In essence there is a supply of warm air being supplied all the time to the area when required.
If the room temperature falls then the heating period is longer and the off period is less so as to try and keep the correct amount of heat flowing into the conditioned space.
Should it get cold enough in the room the elements stay on all the time.
BTW in the 2.5 ton system there are return air vents in each of the three rooms.
There are 2 fresh air systems one of each system that have fans in them to bring in fresh are when required, the smaller system with bring in fresh air when the outside air is cool enough instead of running cooling.
The fresh air system and their fans are installed.
They can be locked on if required, other wise they are on a timer that turns them on once the system is running for short periods.
Now that I can understand since I hoped to get a really cool two story house I found nearby where I live now. I could have gotten the house with one of those Affirmative Action loans that crippled the economy. I knew better than to get tangled up in that mess because I had no backup. All it would take was me winding up in the hospital which actually did happen a few years later. :-(
Although I do not consider domestic air conditioning my field, I would think the majority of home air conditioning years ago here were window units, then non ducted splits systems took over.
In general a home is Australia tend to be single story individual houses locate on their own block of land.
In the larger city where land prices increased there, apartments replaced the individual houses mainly towards the centre of the city, in the larger cities this is increasing as the land price increase.
This has steadily become more prevalent over the last 40-50 years.
The vast majority of apartments are 3 story as if they go any higher elevators must be installed.
As you get closer to the centre of the large city, high rise apartment building are more the norm, than 3 story buildings. This of course is a generalization.
These individual homes tends to make our cities quite large compared to the number if inhabitants.
I have a bit of experience with Australian construction techniques because in the late 1980's I worked out in the Marshall Islands and our prefab housing units came from Australia and I had a hand in assembling them. It was interesting to say the least. ^_^
I have a bit of experience with Australian construction techniques because in the late 1980's I worked out in the Marshall Islands and our prefab housing units came from Australia and I had a hand in assembling them. It was interesting to say the least. ^_^
Prefabs may be used a little in the country, but would be rare.
Mainly homes are built of double brick, brick veneer (Brick outer walls with plaster board inside), Cement brick, some of timber but the timber places seemed to be getting less and less common. There was a period when asbestos was used in some homes on the outer walls but of course that has now long gone, although there would still be many homes like that at around.
Some of of the older homes were constructed of stone. When I lived in Sydney my house was fairly old and made of sandstone blocks.
Multi story apartments are usually cement.
I have seen shots of homes being built in the US using some sort of what appears to be sheets of glued together timber stuff, this is not used here anywhere I have seen.
OK, well if you can keep condensing pressure below 200 PSI, that should be a VERY efficient R22 system.
This electric reheat is a very inefficient way to do humidity control. A dedicated dehumidifier would be a much better setup. Of course, if they never go on, there's no worry, but if they are used much, it would probably pay for a dehumidifier in one season.
Having the system jumping back and forth between heat and cooling will not be efficient. This changeover ought to be a seasonal thing, but may need to be a day/night change, depending on daily temp swings. Better insulation and thermal mass is the best way to fight those swings. It is a total waste of energy to cool during the day and heat at night.
That's panelized construction, the walls and roof are made of huge sheets of plywood with 2x4 studs glued between. Often electrical wiring, insulation and windows are installed at the factory, too. I live in one of these. The only downside is when running wires for phone, network or extra outlets and lights it is hard to snake them through the walls or ceiling.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.