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!