(This posting is not specific to GSHP systems; just an example of what can go wrong with a two zone HVAC system.)
Our old system had 2 furnaces. One for each floor of my home. With the new system we were given either the option of having two GSHP systems or one system with zones. The two GSHP system would have been much more expensive so we went with the two-zone design. Unfortunately, that design did not work out so well. Here's that story of what happened with the zones and how we fixed it.
The Plan
The plan was to have one 4 ton GSHP with two zones. There is a zone damper on each of the two supply trunks. We have two thermostats. When one thermostat calls for heating/cooling or air circulation, that zone damper opens. If they both call, then both zone dampers open. There are were several problems with this design.
Problem #1 is that the air blower on the GSHP was too big for one trunk when only one zone was calling for air.
Problem #2 is that to handle problem #1, they installed a bypass damper to shunt conditioned air from the supply back to the return. In heating season, the bypass also sends heated air back in to the heat exchanger which reduces the system efficiency. In cooling season, the bypass sends cooled air back to the heat exchanger increasing the probability of freezing up the heat exchanger.
Problem #3 is that the bypass damper did not really work properly. It was handling a huge volume of air and bouncing around as the variable blower changed intensity. We were also getting too much air at the vents around the house when the GSHP was in stage 2 (or aux heat, stage 3) and it tells the blower to blow faster (more CFM).
Basically, it was not a good plan.
The fix: disable the zone dampers
I talked to a lot of people. Posted to various message boards. This is the solution that seems to work for us. I really did not like the idea of sending conditioned air around the bypass as we were. So my goal was to avoid that. Some people said to just cut out the bypass and dump the air in to the basement. But my basement is pretty small and we felt the volume of air was too great.
The solution we chose was to disable the zone dampers. The zone dampers we have are power-open/power-close. That means if you remove the power from the dampers, they stay in whatever position they were in when you removed the power. So that's what we did. We made sure both zones were open, and then disconnected the two power wires for the zone dampers.
So instead of sending the "extra" conditioned air around the bypass damper and through the heat exchanger, we are sending the "extra" air to the other zone. If either thermostat calls for heating or cooling then they both get heating/cooling. I may get a manual damper installed to balance the air flow (or partially close one of the zones) to balance the air flow but for now the system seems to be working very well.
Plan C
My installer had another clever idea that we were going to try if the above did not work out. He designed a little circuit to have the system operate as originally intended in stage 1 with two zones and the zone dampers. But if either thermostat was calling for stage 2 heating, which entails more air movement (higher CFM), then his circuit would open both zones. Then we would avoid sending a huge volume of air around the bypass damper only when using stage 2 heating or cooling.
Friday, June 3, 2011
Fixing the cold basement
In addition to having a GSHP to heat the house and make some hot water, we have an ASHP (air-source heat pump) for finishing the job of heating the hot water to 130 degrees F. We have the GE GeoSpring which is a 50g hybrid hot water heater. When in ASHP-mode, the geospring takes heat energy from the space around it -- in my case the basement -- and uses that energy to heat the hot water to the programmed temperature. My geospring is set for 130 degrees F.
The documentation for the geospring says you only need a 700 square foot room and my small basement is slightly more than double that but I suspect the people at GE assumed the space was heated. My basement is not heated. When we had the oil-fired furnaces operating, they were sufficient to keep the basement warm using just the waste heat radiating off the furnaces and flue pipes. Now that they are gone (yippie!) the basement is fundamentally colder (boo!) and then we have our geospring removing any additional heat it can find.
The basement was getting down to 47-49 degrees and that is just too cold. So my HVAC company cut in a manually variable damper. We open it in the colder months to dump a little heat from one of our two zones in to the basement. That seems to be sufficient to keep the basement comfortable. The vent supplies a little heat energy for the ASHP to scavenge to heat the hot water.
When the GSHP is not operating for heating or cooling, the ASHP appears to cost about $1.10-1.70/day to make the hot water we need. The GSHP is often not required during the "shoulders" seasons. (Although this Spring seemed kind of brief!). Normally the input water is about 50 degrees. When the GSHP is being used, the desuperheater warms the input water to 90-110 degrees. That allows the ASHP to work much less to get the output to 130 degrees.
The documentation for the geospring says you only need a 700 square foot room and my small basement is slightly more than double that but I suspect the people at GE assumed the space was heated. My basement is not heated. When we had the oil-fired furnaces operating, they were sufficient to keep the basement warm using just the waste heat radiating off the furnaces and flue pipes. Now that they are gone (yippie!) the basement is fundamentally colder (boo!) and then we have our geospring removing any additional heat it can find.
The basement was getting down to 47-49 degrees and that is just too cold. So my HVAC company cut in a manually variable damper. We open it in the colder months to dump a little heat from one of our two zones in to the basement. That seems to be sufficient to keep the basement comfortable. The vent supplies a little heat energy for the ASHP to scavenge to heat the hot water.
When the GSHP is not operating for heating or cooling, the ASHP appears to cost about $1.10-1.70/day to make the hot water we need. The GSHP is often not required during the "shoulders" seasons. (Although this Spring seemed kind of brief!). Normally the input water is about 50 degrees. When the GSHP is being used, the desuperheater warms the input water to 90-110 degrees. That allows the ASHP to work much less to get the output to 130 degrees.
Winter 2010-2011 Report
We made it through the winter with a few hiccups that I'll attempt to summarize below. Here are my costs for just home heating and hot water for the last few months:
Feb 11 1170 kWh $212
Jan 11 1401 kWh $253
Dec 10 1120 kWh $202
Nov 10 542 kWh $ 98
Oct 10 266 kWh $ 48
Sep 10 254 kWh $ 46
This factors in that I'm paying roughly $0.18 per kWh due to the Nstar 100% Green Energy program surcharges. (It is more like $0.205 now in June).
There were a few days where we used electric heat because of some problems that I'll describe so I'm hoping that the numbers are probably only about $20/month higher than they should have been. I'm still quite happy with this. A six month bill of $859. I'm guessing the next 6 months will be less expensive since the air conditioning is more efficient than the heating. So maybe my annual cost will be in the neighborhood of $1500-$1600. My annual oil bill was typically in the $2400 range + $300 in maintenance. If the savings is only $1000/yr assuming electricity and oil increase in expense roughly similarly, it'll be a while before the system pays for itself. But I'm still quite happy to be off of oil and free frmo the shoddy maintenance of the hurried oil technicians.
Replaced our propylene glycol with ethanol
In March 2011, we flushed out the propylene glycol and replaced it with a 25% ethanol solution called Geosafe. The entering water temp (from the ground back in to the GSHP) -- called the EWT -- was routinely below 40 degrees F. That's okay, except that on the few nights where we were near or below zero, the ground loop froze up and the system reverted to much more expensive electric-only heat. Relative to the propylene glycol, the ethanol solution has better heat transfer characteristics and is easier to pump at very low temperatatures (below 40 degrees). In fact, Climatemaster's flow-center documentation says that they do not recommend propylene glycol for loops below 40 degrees. Propylene glycol gets sludgier and harder to pump the colder it gets (below 40 degrees F.)
I'm told many systems use propylene glycol without problems in New England. I'm guessing that my loop was not sized properly for my home. Another reason installers use propylene glycol is that it is much cheaper than the ethanol (by a factor of 2 roughly, I was told). It is only about 100 gallons of fluid for my wells.
Why was our loop freezing up? Well we are not totally sure. We are extracting more heat from the ground than the loop was designed for. It is supposed to reach a EWT minimum temperature of 30 degrees. But last week (early March) after running for 3 hours in stage 2, it dropped to 29 degrees and showed no sign of stopping. We needed to do a longer test to see where it stabilized -- if at all! -- but given that the system would freeze up after 10-12 hours running on the coldest nights, we think the loop was not able to keep up.
Once the ethanol solution was deployed. I ran a test with the system on its highest setting (stage 2) with the auxillary electric heat disabled. I opened the windows and set the house for 80 degrees and ran it for 7 hours that way. During the test, I plotted the temperature of the entering water temperature -- the water/ethanol solution coming back from under the ground. After about 5 hours, the temperature stabilized at around 35 degrees. That's what you want to see. I believe that I can now run the system indefinitely on stage 2 without the system freezing up. I'm told that GSHP systems are designed to only be able to run in stage 1 indefinitely. Stage one is roughly 2/3s of the total system capacity.
Hot water generator
Other issues: The desuperheater (also called hot-water generator or HWG) was working great all winter. I had a 40gal tank of 110-120 degree water most of the winter. That is, until my HVAC company ran a test, something smoked, and the HWG died. They replaced a card and it started working again. In the process we learned that when the aux electric heat is being called for by the thermostats, the desuperheater disables itself. Usually the technicians say to jack up the thermostats to make the system run, but if that results in a call for the aux electric heat, the desuperheater is disabled. The desuperheater does use some of the heat that would normally go to the house.
Energy Recovery Ventilator
The energy recovery ventilator is working really well. I had some difficulty obtaining filters but my HVAC company has helped out with that. Between the ERV and the ability of the thermostats to circulate the air periodically (without heating or cooling), the air is so very fresh in the house. It is great.
Responsible Installer
My HVAC company had some personnel turn over but they tried real hard to make changes to make my system perform better. They installed the ethanol solution, fixed the HWG card, and added an air vent to my basement -- all for free. (I'll explain the vent in another posting). They had to locate and contract with a more experienced field technician. But that is what you want from a responsible company when you are facing issues with which they do not have enough experience.
Feb 11 1170 kWh $212
Jan 11 1401 kWh $253
Dec 10 1120 kWh $202
Nov 10 542 kWh $ 98
Oct 10 266 kWh $ 48
Sep 10 254 kWh $ 46
This factors in that I'm paying roughly $0.18 per kWh due to the Nstar 100% Green Energy program surcharges. (It is more like $0.205 now in June).
There were a few days where we used electric heat because of some problems that I'll describe so I'm hoping that the numbers are probably only about $20/month higher than they should have been. I'm still quite happy with this. A six month bill of $859. I'm guessing the next 6 months will be less expensive since the air conditioning is more efficient than the heating. So maybe my annual cost will be in the neighborhood of $1500-$1600. My annual oil bill was typically in the $2400 range + $300 in maintenance. If the savings is only $1000/yr assuming electricity and oil increase in expense roughly similarly, it'll be a while before the system pays for itself. But I'm still quite happy to be off of oil and free frmo the shoddy maintenance of the hurried oil technicians.
Replaced our propylene glycol with ethanol
In March 2011, we flushed out the propylene glycol and replaced it with a 25% ethanol solution called Geosafe. The entering water temp (from the ground back in to the GSHP) -- called the EWT -- was routinely below 40 degrees F. That's okay, except that on the few nights where we were near or below zero, the ground loop froze up and the system reverted to much more expensive electric-only heat. Relative to the propylene glycol, the ethanol solution has better heat transfer characteristics and is easier to pump at very low temperatatures (below 40 degrees). In fact, Climatemaster's flow-center documentation says that they do not recommend propylene glycol for loops below 40 degrees. Propylene glycol gets sludgier and harder to pump the colder it gets (below 40 degrees F.)
I'm told many systems use propylene glycol without problems in New England. I'm guessing that my loop was not sized properly for my home. Another reason installers use propylene glycol is that it is much cheaper than the ethanol (by a factor of 2 roughly, I was told). It is only about 100 gallons of fluid for my wells.
Why was our loop freezing up? Well we are not totally sure. We are extracting more heat from the ground than the loop was designed for. It is supposed to reach a EWT minimum temperature of 30 degrees. But last week (early March) after running for 3 hours in stage 2, it dropped to 29 degrees and showed no sign of stopping. We needed to do a longer test to see where it stabilized -- if at all! -- but given that the system would freeze up after 10-12 hours running on the coldest nights, we think the loop was not able to keep up.
Once the ethanol solution was deployed. I ran a test with the system on its highest setting (stage 2) with the auxillary electric heat disabled. I opened the windows and set the house for 80 degrees and ran it for 7 hours that way. During the test, I plotted the temperature of the entering water temperature -- the water/ethanol solution coming back from under the ground. After about 5 hours, the temperature stabilized at around 35 degrees. That's what you want to see. I believe that I can now run the system indefinitely on stage 2 without the system freezing up. I'm told that GSHP systems are designed to only be able to run in stage 1 indefinitely. Stage one is roughly 2/3s of the total system capacity.
Hot water generator
Other issues: The desuperheater (also called hot-water generator or HWG) was working great all winter. I had a 40gal tank of 110-120 degree water most of the winter. That is, until my HVAC company ran a test, something smoked, and the HWG died. They replaced a card and it started working again. In the process we learned that when the aux electric heat is being called for by the thermostats, the desuperheater disables itself. Usually the technicians say to jack up the thermostats to make the system run, but if that results in a call for the aux electric heat, the desuperheater is disabled. The desuperheater does use some of the heat that would normally go to the house.
Energy Recovery Ventilator
The energy recovery ventilator is working really well. I had some difficulty obtaining filters but my HVAC company has helped out with that. Between the ERV and the ability of the thermostats to circulate the air periodically (without heating or cooling), the air is so very fresh in the house. It is great.
Responsible Installer
My HVAC company had some personnel turn over but they tried real hard to make changes to make my system perform better. They installed the ethanol solution, fixed the HWG card, and added an air vent to my basement -- all for free. (I'll explain the vent in another posting). They had to locate and contract with a more experienced field technician. But that is what you want from a responsible company when you are facing issues with which they do not have enough experience.
Thursday, September 2, 2010
Fresh air!
We programmed the thermostats and the ERV (energy recovery ventilator) and we discovered something really nice: The air is really really fresh inside the house. It is almost crisp. I think it is a combination of 3 things:
1) The new system is more appropriately sized for our house. Our old system would blow cold air forcefully and then shut off. The new system seems to be more gentle with its temperature adjustments.
2) The new thermostats have a programmable fan. We have it set to run for 10 minutes every hour if there has been no heat or air conditioning in the last hour. That helps keep the air from getting stale.
3) The ERV is set to run 30% of the time (18 minutes of every hour). When it runs, the ERV takes air from the 2nd floor bath rooms and replaces it with fresh air from outside the house, dumping the fresh air back in to the 2nd floor air supply ducts. If the HVAC system is running, that fresh air will ultimately get circulated throughout the whole house.
1) The new system is more appropriately sized for our house. Our old system would blow cold air forcefully and then shut off. The new system seems to be more gentle with its temperature adjustments.
2) The new thermostats have a programmable fan. We have it set to run for 10 minutes every hour if there has been no heat or air conditioning in the last hour. That helps keep the air from getting stale.
3) The ERV is set to run 30% of the time (18 minutes of every hour). When it runs, the ERV takes air from the 2nd floor bath rooms and replaces it with fresh air from outside the house, dumping the fresh air back in to the 2nd floor air supply ducts. If the HVAC system is running, that fresh air will ultimately get circulated throughout the whole house.
Sunday, August 29, 2010
Desuperheater - making hot water
The GSHP desuperheater has a pump that pulls water from the holding tank, heats it put by 5 degrees and then dumps this hotter water back in to the holding tank. It'll keep doing this as long as it has heat to dump and the water from the holding tank is below a set temperature. The desuperheater can be set to heat the water to either 125 degrees or 150 degrees. 150 degrees is obviously way too hot to have coming out of the tap so we cut the temperature down with a mixing valve that adds cold water. The nice thing about the 150 degree water is that it serves as a nice heat energy storage tank. We use less hot water from the 150 degree tank than we would from 125 degree tank. So we can use a smaller holding tank as well. The hotter the input water to the ASHP, the less work it has to do.
The hot output of the holding tank feeds the cold input of my air-source heat pump hot water heater. The hot output of the ASHP goes to the house. We use the mixing valve to make sure the water we put in to the ASHP water heater is not too hot. That's the grey knob in the center of the picture above.
There are two aspects that confuse me about the mixing valve: One is that because the GSHP runs intermittently we won't get a full holding tank of water at 150 degrees. So I cannot easily configure the mixing valve knob setting. The second issue I have is about the mixing valve itself and how it works. I had two mental pictures for how it worked. The simple picture was that the knob sets the ratio of hot and cold water that get dumped to its output. The more complex picture is that the knob sets the ratio and that the valve somehow senses the temperature and actively varies the ratio between the hot and cold inputs to set the output temperature. I think the reality is somewhere in between. I need to call the manufacturer of the mixing valve to learn more.
Basically, I think there is some sort of temperature sensing element in the mixing valve and it attempts to vary the ratios between the hot and cold inputs over a small range. But if the hot water is too cold, it reaches a limit and mixes in more cold water than it should. For example, if we set the mixing valve for 150 degree input water from the holding tank then it'll probably work fine if the holding tank is at 140. However it will also likely mix in too much cold water if the holding tank is only at 100 degrees.
My plumber was very smart in installing a temperature sensor on the connection between the holding tank and the ASHP water heater. I hadn't thought of that. But now I'm watching it to try to figure out if the mixing valve is set properly. Due to heat leakage from the ASHP, sometimes we see the heat convecting out of the cold input and raising the temperature observed by the thermometer.
There are two aspects that confuse me about the mixing valve: One is that because the GSHP runs intermittently we won't get a full holding tank of water at 150 degrees. So I cannot easily configure the mixing valve knob setting. The second issue I have is about the mixing valve itself and how it works. I had two mental pictures for how it worked. The simple picture was that the knob sets the ratio of hot and cold water that get dumped to its output. The more complex picture is that the knob sets the ratio and that the valve somehow senses the temperature and actively varies the ratio between the hot and cold inputs to set the output temperature. I think the reality is somewhere in between. I need to call the manufacturer of the mixing valve to learn more.
Basically, I think there is some sort of temperature sensing element in the mixing valve and it attempts to vary the ratios between the hot and cold inputs over a small range. But if the hot water is too cold, it reaches a limit and mixes in more cold water than it should. For example, if we set the mixing valve for 150 degree input water from the holding tank then it'll probably work fine if the holding tank is at 140. However it will also likely mix in too much cold water if the holding tank is only at 100 degrees.
My plumber was very smart in installing a temperature sensor on the connection between the holding tank and the ASHP water heater. I hadn't thought of that. But now I'm watching it to try to figure out if the mixing valve is set properly. Due to heat leakage from the ASHP, sometimes we see the heat convecting out of the cold input and raising the temperature observed by the thermometer.
All systems go!
Wednesday August 25th we had power-on for the GSHP system in cooling mode. The good news is that it appears to work. They finished the duct work, control and thermostat wiring, setting the condensate pumps and running condensate drains for my water heater and GSHP. We even tried out the desuperheater and it appeared to generate hot water.In the picture on the right, you can see the 5 "wet" connections for the GSHP. The two copper pipes are for the desuperheater -- to heat the hot water in the white holding tank. The white pipe is for the condensation. You can see a small condensation pump tucked in behind the black insulated pipes. The black insulated pipes go to the red-and-white pumping station on the wall. That's the ground loop pump.
Our old heating system had two completely isolated furnaces. With the new system, we are using the one GSHP. Naively, I thought they'd just make a pair of Y's with the ducts. One for the first and second floor supply vents and one for the first and second floor returns. Reality is a lot more complicated. The HVAC installer really had to be creative to get all the ducts connected properly. Like air origami!
For the first cooling data, we observed the water leaving the GHSP at 74 degrees and returning from the loop at 64 degrees. Given that the ground loop is in 50 degree earth, I sort of expected it to come back cooler, but I guess the analogy is that even an ice cube takes time to melt at room temperature. The good news is that it is cooling. Need more data to see how efficient it will be.
Lots of little things to finish up on the project. Patching holes in walls, fixing a few things here and there. We spread 3 yards of loam and planted some grass over the weekend. We were fortunate enough to have 5 days of rain to get it started. We need to get some more loam. We did not realize that we would be without so much topsoil after the trenching!!
--
Correction to previous posts: they used propylene glycol not ethylene glycol in the ground loop to keep it from freezing in winter. I was surprised: Propylene glycol is used in soaps and even dog food. I think the loop holds about 80 gallons of fluid. About 20 gallons of that is propylene glycol.
Saturday, August 21, 2010
ERV - Energy Recovery Ventilator
The ERV is great for tight homes to bring fresh air in, condition it, and remove stale air from inside the house.
For the inside work, the big surprise was the length of ducts that the ERV requires. It requires 4 connections: (1) fresh air in from outside, (2) waste air to outside, (3) waste air from inside, and (4) fresh air to inside. I should have realized that means a lot of duct work.
The fresh air from outside (#1) is warmed or cooled by the waste air extracted from indoors (#3) and then the fresh air is pumped in to the house (#4). The waste air from inside (#3) has heat extracted from it (in winter) or added to it (in summer) and is then exhausted externally (#2). The 2 external connections have to be at least 10 feet apart and the intake has to be far from other exhaust sources. The standard thing is to run the to soffits or ducts on opposite side of the house. My soffits were too small so we went for opposite sides of the house.
For the #1 and #2 vents, we need external connections. To avoid cutting more holes in the house, we used a small portion of my existing gable vents (about a quarter). Given that I have soffit and ridge vents, we didn't think this would impact attic air flow too much. I also plan to get a couple of mushroom vents installed when I get my roof replaced (that's the next big project!)
What about the inside stuff (#3 and #4)?
The original intention of doing the ERV was to fix the problem I had with the bathroom vents. The current shower fans draped in to the soffits. Since air wants to go in the soffits, not out, all the moist air from the bathrooms would stay inside the house and rise up the roof sheathing. A bad situation. So we didn't use the bathroom shower fans. Really annoying.
With the ERV, we are able to take the exhaust vents from the shower fans and use them as a source of internal waste air (#3). We also took one of the two HVAC air supply lines from the master bathroom (which we had shut off for years) and converted that in to a another source of waste air for the ERV. That avoided cutting another vent hole in my bathroom.
All that remained was to dump the fresh air (#4) somewhere inside the house. The original goal was to split that duct from the ERV and dump half in to the upstairs supply system and half in to a vent on the first floor. But the first floor vent didn't work out; The chase that we had planned to use was full of other duct work and didn't have any space left. So instead, we are just putting the fresh air in to the second floor HVAC air supply system. I'm happy to just have the bathroom shower vent issue resolved! No more opening a bathroom window in the winter!
Avoiding low-resistance cycling
Given that the bathrooms have both HVAC supply vents (where the fresh air from the ERV is being pushed in) and also the waste-air intakes for the ERV, there is some danger of having the ERV just cycle the air in the bathrooms as that would be the lowest resistance path. To avoid that possible loop, we run the fresh air in to the 2nd floor supply system far away from the bathrooms. This way it should reach all the rooms on the 2nd floor. I have my friend Peter to thank for thinking of the issue.
For the inside work, the big surprise was the length of ducts that the ERV requires. It requires 4 connections: (1) fresh air in from outside, (2) waste air to outside, (3) waste air from inside, and (4) fresh air to inside. I should have realized that means a lot of duct work.
The fresh air from outside (#1) is warmed or cooled by the waste air extracted from indoors (#3) and then the fresh air is pumped in to the house (#4). The waste air from inside (#3) has heat extracted from it (in winter) or added to it (in summer) and is then exhausted externally (#2). The 2 external connections have to be at least 10 feet apart and the intake has to be far from other exhaust sources. The standard thing is to run the to soffits or ducts on opposite side of the house. My soffits were too small so we went for opposite sides of the house.
For the #1 and #2 vents, we need external connections. To avoid cutting more holes in the house, we used a small portion of my existing gable vents (about a quarter). Given that I have soffit and ridge vents, we didn't think this would impact attic air flow too much. I also plan to get a couple of mushroom vents installed when I get my roof replaced (that's the next big project!)
What about the inside stuff (#3 and #4)?
The original intention of doing the ERV was to fix the problem I had with the bathroom vents. The current shower fans draped in to the soffits. Since air wants to go in the soffits, not out, all the moist air from the bathrooms would stay inside the house and rise up the roof sheathing. A bad situation. So we didn't use the bathroom shower fans. Really annoying.
With the ERV, we are able to take the exhaust vents from the shower fans and use them as a source of internal waste air (#3). We also took one of the two HVAC air supply lines from the master bathroom (which we had shut off for years) and converted that in to a another source of waste air for the ERV. That avoided cutting another vent hole in my bathroom.
All that remained was to dump the fresh air (#4) somewhere inside the house. The original goal was to split that duct from the ERV and dump half in to the upstairs supply system and half in to a vent on the first floor. But the first floor vent didn't work out; The chase that we had planned to use was full of other duct work and didn't have any space left. So instead, we are just putting the fresh air in to the second floor HVAC air supply system. I'm happy to just have the bathroom shower vent issue resolved! No more opening a bathroom window in the winter!
Avoiding low-resistance cycling
Given that the bathrooms have both HVAC supply vents (where the fresh air from the ERV is being pushed in) and also the waste-air intakes for the ERV, there is some danger of having the ERV just cycle the air in the bathrooms as that would be the lowest resistance path. To avoid that possible loop, we run the fresh air in to the 2nd floor supply system far away from the bathrooms. This way it should reach all the rooms on the 2nd floor. I have my friend Peter to thank for thinking of the issue.
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