Sentinel Kinetic Plus B summer bypass doing nothing

[diarmidR]

Hi all, the summer bypass on our Sentinel kinetic appears to be giving the same inlet temperature as the normal heat-exchange operation. House at 22C, external at 14C and in-flow at vent at 21C in both modes.

 

Has anyone else observed this lack of any temperature drop upon opening the bypass?

 

Ta, D

[Jolo]

In most MVHR units I've seen, the incoming air always flows through the exchanger, it's the exhaust air that flows directly out in bypass mode. So it can take a short while for the heat exchanger to cool down. I assume you've given it time to cool, but I just thought I'd mention this! Another factor to consider is that if the fabric of the house is warm, then the ducting will also be warm, which I find can heat the air up a little as it travels to the vents. I don't know that this would make such an increase as you describe, but it's worth bearing in mind.

 

It might be worth checking that the bypass actually is open too. For example there's an software bug on my Duco MVHR which closes the bypass when the outside temp is below 15°C in "auto" mode, even if the target temperature is set to 10°C! (According to the manual, this forced closing of the bypass is only supposed to happen below 10°C outside temp.) I'm waiting to hear back from them about a software update, but in the meantime I set the bypass mode to "open" instead of "auto" to prevent it from warming up the incoming air. 

[diarmidR]

Thanks @Jolo. When I emailed Sentinel they did mention the possibility that the air would be warming in the ducts as you say. I find it surprising that there is no apparent bypass effect at the vent though. I guess I can test this further by increasing the air flow. Once you open yours, what sort of temperature drop do you see at the inlet vents?

 

I'm currently taking it on faith that the bypass is open when it says it is (it's an auto setting similar to the one you describe - I don't think the unit has an "open" setting). I might test this further by taking the temps at the manifold.

[Jimbo77]

I've been wondering the same. I added some zigbee temperature sensors to the ducts at the top of our Sentinel Kinetic Plus B, in the hopes of being able to see that the summer bypass does do something. 

 

The bypass was turned off for one of the days in the chart below - I can't remember exactly which! 

 

 

We have a gound/air heat exchanger on the inlet side (Rehau Awadukt), and even though the incoming air stays a lot cooler than ambient, the supply side into the house follows the extract side temperature quite closely, no matter what state the summer bypass is in. (The sensors are strapped to the outside of the ducts right where they go in to the MVHR unit, so it's not that the air is being warmed once in the ductwork...)

 

We have the internal temperature target set to 22C, and the limit on the incoming air temperature set to 16C (which, if I've understood correctly, is the point at which it turns the summer bypass off). So even when the internal temp is above the target and the incoming air is cooler (thus the summer bypass should be open - I've also observed it working with the cover off), it makes little difference to the house supply air temperature. It does, however, do a reasonable job of cooling the extracted air before sending it outside... 🙄 

 

It's a shame we miss out on the colder air overnight, but I'll take 21-22C incoming over the 30C+ daytime air temp [literally] all day long... 

 

[Jolo]

5 hours ago, diarmidR said:

Thanks @Jolo. When I emailed Sentinel they did mention the possibility that the air would be warming in the ducts as you say. I find it surprising that there is no apparent bypass effect at the vent though. I guess I can test this further by increasing the air flow. Once you open yours, what sort of temperature drop do you see at the inlet vents?

 

I haven't actually measured it, but it does feel cooler than the ambient temperature inside the house. I'm curious about this myself now, I'll put a temp sensor in one of the vent outlets tonight, and I'll let you know the results!

[Andeh]

Please let us know how you get on!

[Jolo]

Below is the temperature graph for yesterday and today so far (until 2pm CEST).

 

 

I put the sensor into a living room vent outlet at about 7pm (it was in the living room space until then) hence the slight peak at 7pm - the incoming air being a little warmer than the room itself at that time, despite the bypass being closed, as the inlet air will have been around 28°C then.

 

Overnight the unit was on 100% flow the whole time (so I think 42m3/h for this vent), and the bypass was open. The lowest incoming temperature shown is 20.8°C.

 

I don't have anything outside to measure the temp with, but according to the nearest weather station it dropped to about 17°C overnight. So it seems that the air is gaining 4°C between the inlet and the supply vent!

 

I'm not surprised it's little higher, as the wall that the inlet is on does get afternoon sun, which isn't ideal but as it's a retrofit there wasn't any way around that (plus it probably helps warm the incoming air a bit in the winter). So that will be warmer for a start. Internally, this particular vent runs straight down the stairwell and across the downstairs hallway, and is probably 4m in length, so there's not too much scope for heat gain there. (The bedroom ducting runs beneath the flat roof for a couple of metres, so that vent probably has a little more heat gain.)

 

I'm not sure if this helps your original question @diarmidR as there are quite a few variables, including your house being completely different! But given the same outdoor temperature of 14°C as in your original question, with everything else being the same I guess this vent would output 18°C. It's a shame I didn't do this the previous two nights, as the outdoor temp was reported as 12°C, it would have been nice to get a comparison over that temperature range.

[Nestor]

Bit of a ramble,

When the summer bypass is activated, the extracted air is diverted around the heat exchanger preventing this heat from being transferred to the fresh air suppling the home.

I think the supply air on this unit always goes through the heat exchanger. I cannot find a cutaway diagram 

The heat exchanger is effective in winter as I did take some measurements with external temperatures 10c lower than the incoming supply air to the rooms.

 

I checked the summer bypass recently and have fixed it in the open position but makes little difference during the warmer days. I will reinstall to factory settings. 

It might have a minimal cooling effect if the internal temps are lower than external if the bypass is off.

 

For now, this will upset the purists here, I switch off the unit during the day and back on late evening and purge.

Why would I want to input 31c all day when the house has recovered overnight to 21c?

Also a lot of residual heat in the fabric of a well insulated new build might explain the higher supply temperatures.

Shading windows has been the most effective solution for now.

 

 

 

[Jolo]

1 hour ago, Nestor said:

Why would I want to input 31c all day when the house has recovered overnight to 21c?

 

I feel the same way, it seems weird to bring 26°C air into a 23°C room - except my CO2 meter quickly shows that the air quality quickly worsens if the ventilation is turned off.

 

So I set it to the lowest possible that keeps the living room under 1000ppm CO2. This really isn't a lot of air, so I don't feel it heats the room up that much.

 

As you mention, external window shades have made the most difference for us. We now have some form of external shade on all the windows, I'm sure it would be far hotter in here without those!

[Nestor]

19 minutes ago, Jolo said:

 

I feel the same way, it seems weird to bring 26°C air into a 23°C room - except my CO2 meter quickly shows that the air quality quickly worsens if the ventilation is turned off.

 

Thanks, now purchasing a CO2 monitor.

[jack]

2 hours ago, Nestor said:

I checked the summer bypass recently and have fixed it in the open position but makes little difference during the warmer days. I will reinstall to factory settings. 

 

Fixing it in the open position will guarantee to make your house hotter during the day. Bypass should only be used (and should automatically turn on) when the outside temp is below the inside temp.

 

2 hours ago, Nestor said:

For now, this will upset the purists here, I switch off the unit during the day and back on late evening and purge.

Why would I want to input 31c all day when the house has recovered overnight to 21c?

 

Your MVHR shouldn't ever be delivering 31 deg air.

 

In normal, non-bypass mode, the MVHR will work to maintain any existing temperature difference between inside and outside. In summer that means it will transfer most of the heat from the incoming air to the outgoing air, significantly reducing the temperature of the air delivered to the house. So if it's 30 deg outside, and 20 deg inside, the air delivered into the house will be something like 22 deg, depending on the heat recovery efficiency of your unit.

 

Summer bypass only comes on when it's cooler outside than inside. Depending on the unit, you might be able to adjust the temperature at which it kicks in.

 

To maximise effectiveness:

• Reduce airflow when it's really hot outside, cooler inside, and you want to minimise incoming heat. Turn it off if you like, but you risk a stuffy, humid house. Personally I'd avoid that. Summer bypass won't operate in these conditions.
• When the temperature outside drops below the inside temp and summer bypass kicks in, bump up the flow rate to maximise purging.