Duct water heaters/coolers
Posted: Wed Jul 28, 2021 3:56 pm
We have a whole house MVHR system which achieves most of what we hoped for however in very cold weather, or hot weather it could do better.
In cold weather when it is say 0C outside and 20C inside the supply air temperature is between 16C & 18C (80 - 90% efficiency as expected), as the MVHR has no post exchanger heater the supply air to the various rooms is a little too cool.
The house has UFH on the whole ground floor and in the bathrooms (first floor) but nowhere else on the first floor. The UFH is fed from an ASHP via a thermal store. The ASHP supply to the TS comes right beside the MVHR unit. It seems to me that using a duct water heater fed from the ASHP could be used to take the chill off the low air temperature in winter fairly easily.
In summer when it is 20C+ outside the MVHR system bypasses the heat exchanger and sends fresh air into the house as intended. As the temperature outside increases so does the supply air temperature. It strikes me that using a duct water cooler to chill the air when it is to hot would make sense. There are units that will work as both heaters and coolers. I am putting in a rain water harvesting system that I expect to have 5 iBCs below ground so generally at around 10-12C - so thought of using this as a source for cooling.
Question how to plumb the system to use the ASHP in winter and the RWH sytem in summer? The two solutions I am considering are:
1) Replumb twice a year to the "other system" - will lose a little water with antifreeze from the ASHP circuit but that is easily replaced.
2) Use a FPHE with the RWH supply to cool the water in the ASHP circuit that passes through the duct heater/cooler. A pump with the FPHE would be an alternative route avoiding the actual ASHP and TS.
Any better ideas/recommendationS?
In cold weather when it is say 0C outside and 20C inside the supply air temperature is between 16C & 18C (80 - 90% efficiency as expected), as the MVHR has no post exchanger heater the supply air to the various rooms is a little too cool.
The house has UFH on the whole ground floor and in the bathrooms (first floor) but nowhere else on the first floor. The UFH is fed from an ASHP via a thermal store. The ASHP supply to the TS comes right beside the MVHR unit. It seems to me that using a duct water heater fed from the ASHP could be used to take the chill off the low air temperature in winter fairly easily.
In summer when it is 20C+ outside the MVHR system bypasses the heat exchanger and sends fresh air into the house as intended. As the temperature outside increases so does the supply air temperature. It strikes me that using a duct water cooler to chill the air when it is to hot would make sense. There are units that will work as both heaters and coolers. I am putting in a rain water harvesting system that I expect to have 5 iBCs below ground so generally at around 10-12C - so thought of using this as a source for cooling.
Question how to plumb the system to use the ASHP in winter and the RWH sytem in summer? The two solutions I am considering are:
1) Replumb twice a year to the "other system" - will lose a little water with antifreeze from the ASHP circuit but that is easily replaced.
2) Use a FPHE with the RWH supply to cool the water in the ASHP circuit that passes through the duct heater/cooler. A pump with the FPHE would be an alternative route avoiding the actual ASHP and TS.
Any better ideas/recommendationS?