[oldfella]

I saw a claim that in a 8-zone VRV system, and only one zone called, you would essentially get a COP of <=1 since the outside unit couldn't drop below a base level electrical usage.

Is this true, and is this the nature of the beast? Do other systems (e.g. the 2-3 head units) share this "feature"? Do you have to go to the 1-1 head/condensor units to guarantee full efficiency on a 1 zone call?

I realize in some situations this would be unusual for just one zone to call, but it's critical to my usage pattern.

thanks!

 

[mchild]

I saw a claim that in a 8-zone VRV system, and only one zone called, you would essentially get a COP of <=1 since the outside unit couldn't drop below a base level electrical usage.

Is this true, and is this the nature of the beast? Do other systems (e.g. the 2-3 head units) share this "feature"? Do you have to go to the 1-1 head/condensor units to guarantee full efficiency on a 1 zone call?

I realize in some situations this would be unusual for just one zone to call, but it's critical to my usage pattern.

thanks!

I can see how that might be possible, but not terribly probable unless you had a zone that was substantially different in its level of insulation and tightness for infiltration/exfiltration. If that were the case, then it would be to your long term benefit to resolve those issues to not only reduce the occurrence of a one zone call, but to reduce your ongoing energy consumption. If you use any other type of zoning configuration you will have a similar if not worse issue.

I have a four zone VRV system and have one zone that is still having some remediation done with sealing and insulating. It is the oldest part of an old farm house. That zone does call for heat before the other zones and runs the longest, but it does not run solely on its own all that often. Maybe a couple of hours a week during the heating season. During the limited cooling season that I have had the system it has not called once for cooling.

I have monitored my amperage use during many different loads and have seen it run as low as 5.5 amps. This is the equivalent to about 4,600 BTUs of input (5.5amps * 247volts / 1000 = 1.359 kW * 3,414 = 4,640 BTUs). I have to wonder how often you would have only one zone needing less than that for any length of time without another zone having a call too or that zone needing more.

If you went with a 1-1 setup, as a conventional heat pump is configured, then you may well have an over sized unit for the zone or at least it will be over sized for the load. This would cause short cycling which robs efficiency too. It takes 10 - 15 minutes of run time for a conventional heat pump to reach stable system operation and run at its maximum efficiency. Anything less than that and you have a lot of energy being used to produce a little bit of heat.

The beauty of the VRV system is each indoor unit can modulate to the load, which can not be done with the typical multi-head units.

Maybe you could explain your situation in more detail.

 

[jkish]

I can see how that might be possible, but not terribly probable unless you had a zone that was substantially different in its level of insulation and tightness for infiltration/exfiltration. If that were the case, then it would be to your long term benefit to resolve those issues to not only reduce the occurrence of a one zone call, but to reduce your ongoing energy consumption. If you use any other type of zoning configuration you will have a similar if not worse issue.

I have a four zone VRV system and have one zone that is still having some remediation done with sealing and insulating. It is the oldest part of an old farm house. That zone does call for heat before the other zones and runs the longest, but it does not run solely on its own all that often. Maybe a couple of hours a week during the heating season. During the limited cooling season that I have had the system it has not called once for cooling.

I have monitored my amperage use during many different loads and have seen it run as low as 5.5 amps. This is the equivalent to about 4,600 BTUs of input (5.5amps * 247volts / 1000 = 1.359 kW * 3,414 = 4,640 BTUs). I have to wonder how often you would have only one zone needing less than that for any length of time without another zone having a call too or that zone needing more.

If you went with a 1-1 setup, as a conventional heat pump is configured, then you may well have an over sized unit for the zone or at least it will be over sized for the load. This would cause short cycling which robs efficiency too. It takes 10 - 15 minutes of run time for a conventional heat pump to reach stable system operation and run at its maximum efficiency. Anything less than that and you have a lot of energy being used to produce a little bit of heat.

The beauty of the VRV system is each indoor unit can modulate to the load, which can not be done with the typical multi-head units.

Maybe you could explain your situation in more detail.

One configuration that I was interested in might fall into this category.

I was thinking that having the master bedroom/bath on a single zone would allow that zone to have very different temperature settings overnight so you could keep that area as comfortable as you wanted and let the rest of the house be less so.

 

[mchild]

One configuration that I was interested in might fall into this category.

I was thinking that having the master bedroom/bath on a single zone would allow that zone to have very different temperature settings overnight so you could keep that area as comfortable as you wanted and let the rest of the house be less so.

Yes, I can see wanting the master bedroom on its own zone, but I can't see the difference in temp being that great that it would have a big impact on the amount of time that one zone was running alone. Maybe you were assuming that the rest of the home would be on a set back schedule. It would take a rather large set back to impact the whole system. I don't think set backs are a good idea with a heat pump. If there is a set back it should be relatively small and that would minimize the whole issue.

Another thought I had as to the impact on the cost of operation. Daikin can run a use analysis that will project the cost of operation in your real world application. The specific equipment is input, your actual heat gain and loss, and then bin data for your area is used to determine actual usage.

There is no way for the software to know if you have one zone that is going to be calling when no other zone aren't. I have compared my actual usage to the projected for this past winter and it was fairly accurate on the projection. If my one zone that is leaky and not well insulated were causing a lot of one zone run time and greatly impacting the overall COP in a negative way I think I would have seen it in my energy usage.

I don't think the real world is nearly as bad as the OP was suggesting with his question.

 

[jkish]

Yes, I can see wanting the master bedroom on its own zone, but I can't see the difference in temp being that great that it would have a big impact on the amount of time that one zone was running alone. Maybe you were assuming that the rest of the home would be on a set back schedule. It would take a rather large set back to impact the whole system. I don't think set backs are a good idea with a heat pump. If there is a set back it should be relatively small and that would minimize the whole issue.

Another thought I had as to the impact on the cost of operation. Daikin can run a use analysis that will project the cost of operation in your real world application. The specific equipment is input, your actual heat gain and loss, and then bin data for your area is used to determine actual usage.

There is no way for the software to know if you have one zone that is going to be calling when no other zone aren't. I have compared my actual usage to the projected for this past winter and it was fairly accurate on the projection. If my one zone that is leaky and not well insulated were causing a lot of one zone run time and greatly impacting the overall COP in a negative way I think I would have seen it in my energy usage.

I don't think the real world is nearly as bad as the OP was suggesting with his question.

Yes, I was assuming a setback in the rest of the house. In the summer, I could see the MBR at say 75 and the rest of the house at 78 or something like that.

As you say, it may not make enough difference to matter.

 

[oldfella]

Thanks for the real life numbers, that's reassuring. What's the smallest zone you have? Assuming it's about 3/4 ton then I guess that puts you at a respectable 2 COP with worst case of 1 zone running.

The application is a superinsulated 6 family residence with 1 zone cooling and dehumidifying incoming air. Use of the other zones would be very sporadic, but superinsulated houses keep all the heat in by design so even a few computers in a room can become an issue. Everyone gathering in the common room will shift usage to there, etc. Probably not a big deal, but trying to understand my options. I could have more than one condenser, but not looking to litter the landscape with them.

I'm also considering a reverse cycle chiller that would cool zones with water. Overall the refrigerant loop is less expensive and somewhat higher performance in theory, but the water loop system allows the compressor to always run flat out because of the buffer tank. I'm trying to figure out a way I can model the performance of these two solutions.

Of course a zoned air central system is also an option. There will be ducts already for ventilation, but this is a bit of a force fit with the zoned cooling since you don't want to damper off the ventilation air.

 

[mchild]

Yes, I was assuming a setback in the rest of the house. In the summer, I could see the MBR at say 75 and the rest of the house at 78 or something like that.

As you say, it may not make enough difference to matter.

Yeah, I don't think a couple-three degrees too big of a deal. I just don't bother as it isn't enough long enough to make any real difference. I would only have a night set back as the home is occupied during the day.

 

[mchild]

Thanks for the real life numbers, that's reassuring. What's the smallest zone you have? Assuming it's about 3/4 ton then I guess that puts you at a respectable 2 COP with worst case of 1 zone running.

The application is a superinsulated 6 family residence with 1 zone cooling and dehumidifying incoming air. Use of the other zones would be very sporadic, but superinsulated houses keep all the heat in by design so even a few computers in a room can become an issue. Everyone gathering in the common room will shift usage to there, etc. Probably not a big deal, but trying to understand my options. I could have more than one condenser, but not looking to litter the landscape with them.

I'm also considering a reverse cycle chiller that would cool zones with water. Overall the refrigerant loop is less expensive and somewhat higher performance in theory, but the water loop system allows the compressor to always run flat out because of the buffer tank. I'm trying to figure out a way I can model the performance of these two solutions.

Of course a zoned air central system is also an option. There will be ducts already for ventilation, but this is a bit of a force fit with the zoned cooling since you don't want to damper off the ventilation air.

All my zones use ducted air handlers and the smallest is 9,500 BTU, the other three are each 18,000 BTU. Each indoor unit can modulated down to 10% of nominal so they can operate at much lower capacity. Are you planning on using ducted or ductless indoor units?

Have you done a room by room load calc? Determined how much fresh air you need?

 

[oldfella]

Every room is under 9K load (these are small 1 bedroom apartments), so oversizing is inevitable. Fresh air works out to about 130 CFM minimum, although the system will be variable to more than twice that to adjust for occupancy and favorable weather conditions. Why would that matter?

Do you see any other advantage in the systems working together, or did you select a multisplit based having a single compressor footprint?

 

[mchild]

Every room is under 9K load (these are small 1 bedroom apartments), so oversizing is inevitable. Fresh air works out to about 130 CFM minimum, although the system will be variable to more than twice that to adjust for occupancy and favorable weather conditions. Why would that matter?

Do you see any other advantage in the systems working together, or did you select a multisplit based having a single compressor footprint?

The fresh air introduction will impact the load - that's why I asked. Is the cooling and heating load about the same? Six apartments with common areas too? Are the common areas also in the 9K range? Sounds like you may need two outdoor units.

When I purchased my old farm house a few years ago it had grossly over sized equipment and huge energy bills. As I researched alternative ways to condition the air it became clear that a heat pump was the most efficient way of doing so. I became intrigued by variable capacity systems and found they had been used around the world for decades. Cheap energy costs had kept them out of the US, but that wouldn't continue.

I like the fact that the air handlers were physically small and had a broad range of capacities to choose from. When designing the system, having zones based on the building diversity was a great option. An added benefit was the increased output and operating efficiency of the system as the connection ratio increased.

The outdoor unit is very quiet as I can not hear the compressor running. During heat cycles you can hear air moving as the two fans are in high speed, but during cooling cycles the fan speed modulates and is normally lower so you rarely hear it at all. Nice for summer outdoor activities. You can stand right next to the unit and have a conversation with out raising your voice.

The sophistication of the communications and self diagnosis is very impressive. The system will not run if there is a fault that could be damaging. The fault will lead you to the problem. Other than changing air filters there really is nothing that needs to be done for maintenance.

I did my research and found Daikin to be a high quality manufacturer with strong support for the technician and the homeowner/end user. Its the same reason I drive cars made under the Toyota brands.

 

[snugglepuppy666]

just a question and comment..

VRV is a Daikin trademarked name for the domestic market.

VRF is the correct terminology for any of the variable refergriant flow systems. the only 4 in the states are Mitsubishi, LG, Sanyo and Daikin.

I have personel experience with Daikin and LG.

FYI Daikin is Japanese by design BUT it is currently assembled in Taiwan (see the sticker on the box) and soon to be Vietnam due to labor costs.

LG is S. Korean designed and made.

Mitsu is a decent product too.

With Daikin your paying for the name and the hype. They were here in the 80's and pulled out. Burned a lot of contractors. Still come across people who wont touch it.

My affiliation:

http://www.hughcunningham.com/hvac.html

The current LG rep and former Daikin rep.

 

[oldfella]

snugglepuppy, do you have any insight on how well the LG VRF system behaves when presented with a load from a single zone? Are units like the LG Tri Zone pretty much the same, or are they fundamentally better or worse for this? Is it correct to assume that a tri-zone unit has just one compressor?

Is it practical to have some external control of these units (e.g. computer over LonWorks) to, for example, control them to not call from just one zone. For example, assume you had several apartments hovering at their set point, and one busting over because of some large plug load. Since you are running the compressor anyway, it might be more efficient to cool some other zone that wasn't calling, but could accept some cooling. Does their programming already handle this?

 

[oldfella]

I found the post that prompted my line of inquiry on another board:

"The house heat is supplemented by human activity and solar through the windows and the garage isn't. But the condenser power in bottoms out at about 6000 Btu anywhere below 50% load. If my garage unit is idling just keeping up with heat loss, which is about 6000 Btuh I have an effective COP around 1."

Clearly dmaceld was happy with his VRF system, but would have designed it differently if he understood better how the system was going to work before he installed it. He notes "I should have used a 12 or 18 KBtuh unit in the garage". This 2x or 3x oversizing would have allowed him to both use the extra condenser capacity and to get his garage unit to cycle off more. Smart.

(http://www.greenbuildingtalk.com/Fo...alk.com/Forums/tabid/53/forumid/13/postid/43541/view/topic/tpage/1/Default.aspx)

Of course the oversizing strategy presumes you can predict which load point will likely call by itself, and can size the wall unit appropriately. Also it would reduce the ability of the system to dehumidify.

 

[snugglepuppy666]

snugglepuppy, do you have any insight on how well the LG VRF system behaves when presented with a load from a single zone?

1 zone or 3 it dosnt matter. There are 2 compressors up to 4. one is a static state comp the other is a freq drive. so take the rated tonage and divide by 2. SOOOO 4 tons vrf 2 ton freq modulates down. 24kbtu calling for 12k is only 50% reduction. the freq will work down to 30%. Above 60% the static state kicks on and the freq modulates to the minimum.


Are units like the LG Tri Zone pretty much the same, or are they fundamentally better or worse for this? Is it correct to assume that a tri-zone unit has just one compressor?[/QUOTE]

The inverted based platforms will moudlate the same way. the catch is you cant oversize based on zoning diversity.

they have 2 compressors but they require in individual linesets.

Is it practical to have some external control of these units (e.g. computer over LonWorks) to, for example, control them to not call from just one zone. For example, assume you had several apartments hovering at their set point, and one busting over because of some large plug load. Since you are running the compressor anyway, it might be more efficient to cool some other zone that wasn't calling, but could accept some cooling. Does their programming already handle this?[/QUOTE]

Yes and No. you can use full BACnet or Lonworks or a standalone controller localized while offering the ability to control from each room within the parameters set by the master.

kind of confused on the last part. the zone wont call for cooling unless the return air thermistor deems it necessary.

what exactly are your BTU requirements for each zone? Load calcs? Where are you located.

Hope i helped

 

[snugglepuppy666]

Of course the oversizing strategy presumes you can predict which load point will likely call by itself, and can size the wall unit appropriately. Also it would reduce the ability of the system to dehumidify.

will address the rest later but.

it all boils down to load at a given time of day. East West diversity. expected load at given time. total btus available. Load shifting is the concept

the ability to dehumidity will not be affected. there are 3 speeds on the VRF based systems (indoor). As it gets close to satisfying it will step down. Short cycling isnt a problem WITHIN reason. The inverter splits have variable speeds.

also note that there is HRV vs HP. application is key.

 

[oldfella]

kind of confused on the last part. the zone wont call for cooling unless the return air thermistor deems it necessary.

My point was that this might not always the best strategy. For example when the 6000 btu unit calls, the system "knows" that there will be capacity wasted answering just that zone. If it considered, say, a low set point of 68, and a high set point of 78, it could cool rooms below their high set point for little or no extra cost. Apparently some zoned forced air systems do this.


The buildings are still being designed, but roughly consider them to each have 7 500 square foot 1 bedroom apartments + 1 500 square foot common area. Buildings will be superinsulated with triple glazed windows and various techniques to reduce solar gain. Mixed-humid climate, Philadelphia.

 

[Shophound]

I'm also considering a reverse cycle chiller that would cool zones with water. Overall the refrigerant loop is less expensive and somewhat higher performance in theory, but the water loop system allows the compressor to always run flat out because of the buffer tank. I'm trying to figure out a way I can model the performance of these two solutions.

The load on a compressor serving a chilled water buffer tank will vary as the split between the entering and leaving chilled water varies. Water has good thermal properties (somewhat diminished if glycol must be used to prevent the chilled water loop from freezing), and for human comfort cooling purposes, the loop temperature can swing a bit without adversely harming the desired interior environment.

With a chilled water system you could actually accomplish humidity control with controls that override the discharge air temperature setpoint of a fan coil or air handler if there's a humidity sensor in the return air stream. Each fan coil could have three way valves for modulation of chilled water through the coil, and the blower could run continuously to provide air circulation, filtration, and good temperature/humidity control with less fluctuation. These methods are used in commercial applications, where tighter humidity and temperature control are desirable. Continuous blower operation can add to cost of operation, however.

 

[oldfella]

I agree that chilled water sounds like a great system all the way around, but unfortunately it works out to be even more expensive than VRV/VRF. The number of suppliers for residential class chillers in the US is small; I've found Multiaqua, Aqua Products, and Unico. Daikin, Mits, and others have interesting looking inverter based mini chillers (even CO2 based) but they don't offer them here. I understand that some HVAC pro's (that would not be me) will make their own chiller by replacing the indoor coil on a standard split system with a chiller barrel. Probably cost effective if you do it yourself, but probably not to hire it done.

I especially like the way the Aqua Products reverse cycle chiller is packaged: it combines a buffer tank and circulation pump with the chiller barrel and outdoor compressor. It switches easily between heating and cooling. It's expensive, and the number of dealers is small.

I like the fact that chilled water systems are both old and still going strong (in the commercial world at least). I get the impression that current R410a designs could be just be another throw away like R22. Transitioning to CO2 mini-splits, for example, would require pulling all new piping through the building; replacing a R410a chiller with a CO2 chiller or even some future LiBr solar chiller would be an hour's work.

First costs of VRF are lower than chilled water, and I'm told the cooling coils are significantly colder than chilled water systems which all else being equal would be better for dehumidification. VRF units seem to have above average controls out of the box, but perhaps harder to exert your own controls on (compared to relatively easily controlled water and air systems).

You can't beat the first costs of central air/heat pump. I wish I really trusted the ability of forced air zoning to keep everyone comfortable. Every forced air system I've experienced has been a perpetual war of hots and colds.

So chilled water, VRF, or forced air? It's a tough choice.

 

[mchild]

I found the post that prompted my line of inquiry on another board:

"The house heat is supplemented by human activity and solar through the windows and the garage isn't. But the condenser power in bottoms out at about 6000 Btu anywhere below 50% load. If my garage unit is idling just keeping up with heat loss, which is about 6000 Btuh I have an effective COP around 1."

This individual does not understand the the definition of COP. It is the energy consumed to produce the needed BTUs.

With VRF/VRV systems the COP increases as the compressor operates at lower capacities. In other words, it takes relatively less electricity to make the needed BTUs at part load than at full load. One manufacture shows a schedule that their unit consumes 33% of the electricity at 50% load compared to the compressor producing its nominal load.

 

[snugglepuppy666]

My point was that this might not always the best strategy. For example when the 6000 btu unit calls, the system "knows" that there will be capacity wasted answering just that zone. If it considered, say, a low set point of 68, and a high set point of 78, it could cool rooms below their high set point for little or no extra cost. Apparently some zoned forced air systems do this.


The buildings are still being designed, but roughly consider them to each have 7 500 square foot 1 bedroom apartments + 1 500 square foot common area. Buildings will be superinsulated with triple glazed windows and various techniques to reduce solar gain. Mixed-humid climate, Philadelphia.

aaahhhhh got you now. .. I think your concern is irrelevant..

1) temp diff set points. system knows nothing but what the sensors tell it. as mentioned earlier. if your not grossly oversized you should be ok

2) there is no capacity waste because the comp is an inverter. no/minimal start up load.

on the other hand....

anyone addressing fresh air introduction? that to me is a bigger concern than temp diff and wasted energy in an ultra tight building.

also, in an apartment i HOPE this is a heat recovery system! if not how do you deal with the fact that 1 of the 20 tenants is having hot flashes and wants the system on cool when its 60 outside?

also again, you gain no advantage w/ diversity in an apartment setting. I feel you need to size based on max load. there is no telling who is going to leave the AC @ 60deg when they leave for the day.

many things to think about.

1) customer comfort
2) equipment life
3) cost vs payback
4) efficency

hope this helped