Residential Load Calc for Daikin VRVIII-S

[gschra11]

Howdy folks,

I'm applying a Daikin VRVIII-S to my house. I've run loads for four zones in my home and want opinions as to what equipment size I end up going with.

Zone 1: Bedrooms
12.6 MBH Cooling, -19.9 MBH Heating

Zone 2: Family Room
14.8 MBH Cooling, -13.2 MBH Heating

Zone 3: Living Room/Dining Room
13.5 MBH Cooling, -18 MBH Heating

Zone 4: Man Cave (Basement)
6.3 MBH Cooling, -8.7 MBH Heating

My block load for the house is 3.8 tons and -59.7 MBH. Design temps are -2°F heating, 96°/76° Cooling.

I have selected the 4-ton outdoor model with the first three zones selected as 18 MBH FXMQ_PVJU fan coils and the Man Cave with a 9 MBH FXMQ_PVJU. This gives me approximately a 130% diversity.

Does this sound like what you would do? The only reason I ask is because of the cooling. I'm going with 18 MBH FXMQs because of the heating load, not the cooling load. I figure if the unit is capable of modulating down to meet the load, then I had might as well give the system the coil size and outdoor unit size to put out as much heating as I can in the winter to avoid having to use my supplemental heat strips as much as possible. This does not follow normal heat pump sizing rules, but I figure the rules don't apply here because of the nature of inverter compressors.

Thoughts?

Also, for those who have installed/service/use these machines, please let me know what you love/hate about them. Yes, I know, it's a loaded question.

Thanks!

[teddy bear]

In green grass climates and with heat pumps, size for the heating loads. The a/c will be usually be oversized. Set the a/c for a coil temperatue 6-8^F colder than the desire inside dew point. 75^F, 50%RH is a 55^F dew point and the a/c coil temperature should be 47^F. During low/no cooling loads, supplemental dehumidification is needed to maintain <50%RH with all the VS speed a/cs. A small whole house dehumidifier is an excellent addition, if you want <50%RH during all of the seasons in your climate. Ultra-Aire/Honeywell are a couple of the mfgs. I would also suggest a small amount of fresh air when the home is occupied during the calm times of the year. This combination of filtered fresh air and <50%RH provide a ideal comfort and indoor air quality.
Regards TB

[mark beiser]

Looks like you have a good handle on the sizing of the air handlers.

Also, for those who have installed/service/use these machines, please let me know what you love/hate about them. Yes, I know, it's a loaded question.

My only real complaint is how wide the 18 and 24 MBH FXMQ_PVJU air handlers are, I wish they would fit in the same space as a First Company fan coil unit does.

Other than that, make sure you install them with a few extra inches of clearance on the service access side, and that you have a clear shot up through the bottom, or you will be hating life when you have to service them.

[mchild]

Howdy folks,

I'm applying a Daikin VRVIII-S to my house. I've run loads for four zones in my home and want opinions as to what equipment size I end up going with.

Zone 1: Bedrooms
12.6 MBH Cooling, -19.9 MBH Heating

Zone 2: Family Room
14.8 MBH Cooling, -13.2 MBH Heating

Zone 3: Living Room/Dining Room
13.5 MBH Cooling, -18 MBH Heating

Zone 4: Man Cave (Basement)
6.3 MBH Cooling, -8.7 MBH Heating

My block load for the house is 3.8 tons and -59.7 MBH. Design temps are -2°F heating, 96°/76° Cooling.

I have selected the 4-ton outdoor model with the first three zones selected as 18 MBH FXMQ_PVJU fan coils and the Man Cave with a 9 MBH FXMQ_PVJU. This gives me approximately a 130% diversity.

Does this sound like what you would do? The only reason I ask is because of the cooling. I'm going with 18 MBH FXMQs because of the heating load, not the cooling load. I figure if the unit is capable of modulating down to meet the load, then I had might as well give the system the coil size and outdoor unit size to put out as much heating as I can in the winter to avoid having to use my supplemental heat strips as much as possible. This does not follow normal heat pump sizing rules, but I figure the rules don't apply here because of the nature of inverter compressors.

Thoughts?

Also, for those who have installed/service/use these machines, please let me know what you love/hate about them. Yes, I know, it's a loaded question.

Thanks!

I installed my VRVII-S in the fall on 2008, so I have now lived with it through several cooling and heating seasons. Like you I have the 4 ton system with three 18K indoor units and one 9.5K indoor unit. All ducted units. First thing I found that was not as expected is the lack of auto fan on the indoor units. Documentation was not clear on that and while some Daikin units do have auto fans, I don't think any of the indoor units used with VRV. I noticed you are using the newer P series ducted units and they may have added the auto fan function to that unit. But you may want to look into that.

Without auto fan I have to manually set my blowers based on the anticipated load. In cooling if I leave to blowers on High de-humidification suffers. I keep the blowers on Low unless I expect the temp to rise to a certain point when I then move the blower speed to High (I also use the Dry mode a fair amount). I am in the Mid-Atlantic area so summer humidity control is an ongoing issue. To further help with that I have set the target cooling coil temp to the lowest setting (through the Setting Mode 2 on the outdoor PCB). I have also set the target coil temp for heating at the highest point.

Additionally, I found the continuous running of the indoor blower annoying and during cooling cycles the re-evaporation of condensation was an issue. With my indoor units I was told there was no way to cycle the blower off when the cooling temp was reached. I found there is, in fact, a setting for the blower to cycle off. Same thing in heating mode. Fan dropped to lowest speed in the off cycle but if any other units were heating then the refrigerant continued to pass thorough all indoor coils (for oil return purposes) and heating continued in those zones that were no longer calling. Significant overheating occurred. Getting the indoor blowers to cycle off resolved that.

You mention using strip heat for auxiliary/supplemental heating. How will you control this secondary heat source? Seems like you will have a fairly high usage of strip heat. While these systems do provide significant heat at lower ambient temps your use of strip heat may be significant. My design temp is not as low as yours (9*F) but your heat loss seems like it is proportionally similar. I am able to maintain my indoor temp down to about 15*F - without excess winds, with the heat pump and below that the use of strip heat to supplement the heat pump. Your system should do a little better (VRVIII has higher heat output). If you have not done it, you may want to have Daikin run your setup through their software and they can tel you what the adjusted heat output will be for each indoor unit at your design temp.

The outdoor units can move some big air through them when both fans are on high. The two fans are always on high in heat mode and will run continuously at night when temps are the lowest. Consider this when deciding the placement of the outdoor unit and its proximity to bedrooms and other areas that might be impacted by the sound. Not near as much of an issue in the summer. I used remote temp sensors in each zone and placed all my controls in a first floor utility closet. Nice clean install.

Overall, the cost to run my system has saved me about $2,000 per year and the home is much more comfortable. The previous systems were grossly oversized, ran short cycles, and created large temp swings.

[teddy bear]

In green grass climates with seasons with low/no cooling loads and outdoor dew points that are +55^F, consider the addition of small whole house ducted dehumidifier. These unit are able to maintain <50%RH when the a/c does not run enough to remove moisture from the infiltrating fresh air and the occupants. Units like the Ultra-Aire/Honeywell/etc are designed for remote %RH sensing. In addition the are able to add a small of amount filtered fresh air to the home during occupancy and low natural ventilation.
Keep us posted on your results.
Regards TB

[gschra11]

Thank you for all of the input.

To comment and respond to some posts, the ducted units that I will be using ("P" series) I have confirmed have an "Auto" fan mode, although, curiously, the mode only shuts the fan down when heating or cooling are not being called for.* Otherwise, it is a constant volume fan set to whatever you commissioned it to on day one. (Of course you get the three speeds) The Daikin rep tells me that custom control work would allow me to change fan speeds as demand increased or decreased, but such work is cost-prohibitive. That being the case, at least I won't suffer from the overheating mentioned as the fan won't run when there is no call.

Electric strip heat is going to be a custom job on my part. Duct heaters will go into three of the four units. I will wire relays to them to an existing programmable thermostat that I plan to set slightly lower than the setpoints of the Daikin stats in the house. When the thermostat calls, it will "enable" the heat strips. Then, there are airflow switches in the three fan coils. If a zone is satisfied, the air stops and the switch trips, disabling that unit's heat. Otherwise, the airflow kicks the strip on and heats the zone. I could have gone with Daikin's electric strip control board, but Daikin itself didn't recommend it. Apparently, it kicks strips on 7° below setpoint and kicks them off 3.5° below setpoint. They said its a bad design that they are going to fix eventually and pretty much wouldn't sell it to me.

mchild, it sounds like our houses are quite similar. I'm replacing because my system is grossly UNDERSIZED. The previous owner built an addition and connected to the existing system. I have a 2 1/2 ton unit for a house with nearly a 4-ton block load! Therefore, I do not expect energy savings, even with such a sophisticated machine. I do, however, hope to address the undersizing issue and also the zoning issue that goes along with an addition that is slapped on to an existing system. Did I mention there were no balancing dampers anywhere?

The humidity scares me. I'm in Kansas City. I live in the middle of the Gulf Stream.

I will keep you all posted. Installation will occur in three weeks, after the weather cools down a little.

*Sidenote: The only VRF manufacturer that I have found that has true "Auto" fan functionality is Mitsubishi, but only on their 3x3 4-way cassette. It will actually automatically change fan speeds and turn the fan off based upon thermal load. Why they chose to do this on only this model and why no other manufacturer touches it at all is beyond me.

[mchild]

Thank you for all of the input.

To comment and respond to some posts, the ducted units that I will be using ("P" series) I have confirmed have an "Auto" fan mode, although, curiously, the mode only shuts the fan down when heating or cooling are not being called for.* Otherwise, it is a constant volume fan set to whatever you commissioned it to on day one. (Of course you get the three speeds) The Daikin rep tells me that custom control work would allow me to change fan speeds as demand increased or decreased, but such work is cost-prohibitive. That being the case, at least I won't suffer from the overheating mentioned as the fan won't run when there is no call.

Electric strip heat is going to be a custom job on my part. Duct heaters will go into three of the four units. I will wire relays to them to an existing programmable thermostat that I plan to set slightly lower than the setpoints of the Daikin stats in the house. When the thermostat calls, it will "enable" the heat strips. Then, there are airflow switches in the three fan coils. If a zone is satisfied, the air stops and the switch trips, disabling that unit's heat. Otherwise, the airflow kicks the strip on and heats the zone. I could have gone with Daikin's electric strip control board, but Daikin itself didn't recommend it. Apparently, it kicks strips on 7° below setpoint and kicks them off 3.5° below setpoint. They said its a bad design that they are going to fix eventually and pretty much wouldn't sell it to me.

mchild, it sounds like our houses are quite similar. I'm replacing because my system is grossly UNDERSIZED. The previous owner built an addition and connected to the existing system. I have a 2 1/2 ton unit for a house with nearly a 4-ton block load! Therefore, I do not expect energy savings, even with such a sophisticated machine. I do, however, hope to address the undersizing issue and also the zoning issue that goes along with an addition that is slapped on to an existing system. Did I mention there were no balancing dampers anywhere?

The humidity scares me. I'm in Kansas City. I live in the middle of the Gulf Stream.

I will keep you all posted. Installation will occur in three weeks, after the weather cools down a little.

*Sidenote: The only VRF manufacturer that I have found that has true "Auto" fan functionality is Mitsubishi, but only on their 3x3 4-way cassette. It will actually automatically change fan speeds and turn the fan off based upon thermal load. Why they chose to do this on only this model and why no other manufacturer touches it at all is beyond me.

I guess I'm not completely sure what the Auto fan function on the P series air handler does. Does it not change the blower speed as the load in the space changes? Yes, I know Mitsu has Auto fan but thought it was across their line of indoor units suitable for their VRF system.

You are being good advice on the Daikin add-on control board (KRP1B71) that can operate the supplemental heat. The temp spread should be programmable (as the Mitsu system is) and they have known for years it needed to be addressed. I have used the KRP1B71 add-on board along with base line HW VP 8000 stats to control in-duct strip heat. The KRP board has a connection point that closes when the blower is running. I ran the strip heat control wire from the stat through the KRP board and then the the strip heat. Then, when there is a call for strip heat it can only switch on the heater if the blower was running - same as your air flow switch. This allowed for supplemental heat and if the outdoor unit was not functioning I could place the indoor unit in fan mode and run just the strip heat as emergency heat. I did not want the risk that the strip heat could cycle on without the blower running. I set the HW stat temp 2* below the Daikin temp. Because the Daikin system uses 20K ohm thermisters and the HW use 10K, they don't always read the same so to keep the strip heat from coming on prematurely you may have to set a larger delta than you are anticipating. Also, the Daikin system does not maintain the temp swing in the space as tight as we have become accustom to with U.S. based controls that keep it within one-half of a degree.

I have found that the strip heaters for the two air handlers on the second floor of the home rarely if ever have a call to supplement. But I have had to use them as emergency heat so well worth having. The only times I have had to use the strip heaters as emergency heater is when the outdoor unit was off for many hours during a big snow dump and we lost power (still thinking I should get a generator). Daikin insists that you have power to the outdoor unit (crankcase heater) for six hours before firing the compressor up.

As I mentioned before, I installed all controls in a closet. I have remote temp sensors for the Daikin equipment and remote sensors for the HW stats. I used the HW remote sensor housings and put both sensors in that one housing. I thought they looked better.

The dry mode works fairly well. It does not function based on humidity it simply cycles the indoor unit in cooling mode at the low fan setting. I have not been able to find the documentation to support it but, I think it sets a lower target temp for the indoor coil when in Dry mode in order to maximize moisture removal. It will attempt to maintain the temp that was in the space at the time the indoor unit was placed in Dry mode. It will also over cool the space up to about 3*F. So, if the space is too cool, Dry mode will not function until the space warms up. In milder weather I have found that just leaving some of the zones in Dry mode will keep the humidity levels comfortable (45% or less) and maintain temp when the ambient swings up. Right now the outdoor temp is 77* and the RH is 87% while the indoor conditions are 76* and RH of 47%.

Full documentation of these systems does not exist. Daikin tech support has lots of knowledge that is not available in all the documentation. There is a lot these system can do or be programed for that is not readily available.

I hope this helps and if you have any questions I'll be glad to try and answer them.

[mark beiser]

IThe KRP board has a connection point that closes when the blower is running. I ran the strip heat control wire from the stat through the KRP board and then the the strip heat. Then, when there is a call for strip heat it can only switch on the heater if the blower was running - same as your air flow switch.

You can also use the "humidifier" connection on the KRP board to operate the supplemental heat. The board powers the humidifier connection any time there is a call for heat, so you can use that output through an outdoor thermostat, set to close below the temperature you need/want the supplemental heat strips to come on with the heat pump, to turn them on.
I'll have to double check, but I'm pretty sure that when the heat pump is not working, the supplemental heat contacts on the KRP board will close on any call for heat, instead of waiting until the indoor temperature is 7º below the set temperature.
You don't need to have a 2nd indoor thermostat to run the supplemental heat.

If you put in an outdoor thermostat wired in parallel with the Honeywell thermostat you are currently using, you would have automatic supplemental heat when the outdoor temperature is near or below the balance point, and still have your emergency heating work the way it does now.

You are correct that they don't really fully document all of the possibilities, but they do list how all of the inputs and outputs operate, it just takes a little imagination to combine the available options to get what you want.

[mchild]

You can also use the "humidifier" connection on the KRP board to operate the supplemental heat. The board powers the humidifier connection any time there is a call for heat, so you can use that output through an outdoor thermostat, set to close below the temperature you need/want the supplemental heat strips to come on with the heat pump, to turn them on.
I'll have to double check, but I'm pretty sure that when the heat pump is not working, the supplemental heat contacts on the KRP board will close on any call for heat, instead of waiting until the indoor temperature is 7º below the set temperature.
You don't need to have a 2nd indoor thermostat to run the supplemental heat.

If you put in an outdoor thermostat wired in parallel with the Honeywell thermostat you are currently using, you would have automatic supplemental heat when the outdoor temperature is near or below the balance point, and still have your emergency heating work the way it does now.

You are correct that they don't really fully document all of the possibilities, but they do list how all of the inputs and outputs operate, it just takes a little imagination to combine the available options to get what you want.

In looking at the KRP board schematics I had the thought that the humidifier terminals might work that way. Here is why I decided to go with separate stats - my home is an old farm house and somewhat loose in its construction. I can have a relatively large swing in outdoor temps when the supplemental heat is called for depending on the amount of wind. With low/no wind I can get to 14-15* before I need supplemental but on a windy day the ambient could be a lot warmer out but I could need the supplemental. So, without a way to call for the supplemental based on actual indoor temp means either I am using supplemental when I don't need to or it is not coming on when I do need it.

I thought in order to have the KRP board function as you suggest you had to make programing changes to lock out the heat pump. I needed to keep my system simple enough that when I wasn't available other family members could get the system up and running with a few instructions if something out of the ordinary happened.

Also, the KRP board has contacts that close (not powered) anytime the compressor is running which could be used in a similar fashion as the humidifier terminals. This set of contacts would close in both cooling and heating mode.

[gschra11]

I guess I'm not completely sure what the Auto fan function on the P series air handler does. Does it not change the blower speed as the load in the space changes? Yes, I know Mitsu has Auto fan but thought it was across their line of indoor units suitable for their VRF system.

Yeah, I was a bit befuddled as well, but the Daikin guy tells me that the only thing "Auto" about the fan is that the fan goes off when the stats no longer call. Otherwise, they are running on whatever the fan speed is at the thermostat. (HH, H, M)

The only Mitsubishi unit that has the speed control listed in their documentation is the 4-way cassette. That isn't spelled out for any other indoor unit that I saw.

[mchild]

Okay, I think that might be stretching it a bit to call that an Auto function. I thought on that unit you got the fan to go off when the call was satisfied by simply using regular Field Codes (12-6-3 for cooling and 12-3-3 for heating). With my indoor units I had to access the top secret 50 codes to get the fan off in cooling mode.

Setting up the system for auto changeover of heating and cooling can be a little challenging too. Let me know if I can help but it sounds like you have a good contact with Daikin. Also, it sounds like a number of these types of issues have been dealt more effectively with the newer P series equipment and the Navigation controller than the previous generation that I have.

[mark beiser]

The navigation controller is worlds better than what was available when you got your VRVII-S system.
In addition to much easier programing of setbacks, there are a number of options that can be switched around via menu selections, rather than having to muddle through function codes.

Of course the best thing about it is that it can be set to show the actual room temperature and the set temperature at the same time!
For some reason, Japanese HVAC engineers don't seem to understand why us crazy Americans want to be able to see that. I've had conversations with 5 different engineers from 3 different manufacturers, and they all seemed confused as to why we want both to be displayed.

[mchild]

The navigation controller is worlds better than what was available when you got your VRVII-S system.
In addition to much easier programing of setbacks, there are a number of options that can be switched around via menu selections, rather than having to muddle through function codes.

Of course the best thing about it is that it can be set to show the actual room temperature and the set temperature at the same time!
For some reason, Japanese HVAC engineers don't seem to understand why us crazy Americans want to be able to see that. I've had conversations with 5 different engineers from 3 different manufacturers, and they all seemed confused as to why we want both to be displayed.

I originally thought it would work to control multiple indoor units with only one of the older style controllers (BRC1D71). I have since stepped up to having individual controllers for each indoor unit and used the Navigation Controller - but still have and use one of the old controllers. The Navigation Controller is a big step toward improvement. Back when I first got my system up and running, somehow one of my indoor units got locked into Low blower speed. No where in the documentation is it mentioned that this can be done or how to undo it. Only one person in Daikin tech support had ever heard of it and eventually figured out how to unlock it. For some reason my Navigation Controllers don't give me things like the outdoor temp, the indoor unit status various temp sensor readings, and such.

In the early years of Mercedes Benz being imported to the US, their engineers could not figure out how the crazy Americans could use both a/c and a sun roof. They originally just installed the sun roof as they do in Germany. American dealers kept telling them they had to put a/c in the cars. Finally, they got a group of engineers to come over here and they took them for a drive - guess where. Through Texas in the summer. The German engineers quickly agreed that a/c was a must and said they could put it in instead of the sun roof. They were told add the a/c and keep the sun roof. They thought the Americans were down right crazy to need and/or want both. Japanese engineers probably agree with them.