HRV & Hot water duct booster coil

tippgaafan

Just looking for opinions on the following idea.
With HRV running, if a sufficient heat source is not maintained, the overall temperature of the house will reduce. At night most people turn off the boiler. I had a notion of installing a hot water duct booster coil (similar to car radiator) on the return air duct to a HRV unit. The coil could be heated from boiler etc. The boiler could be left on overnight with HRV zoned seperate from radiators\cylinder. This would keep the supply air temperature at a comfortable level and boiler would not be cycling too often due to small volume of water.
I have'nt located any performance curves of these coils. I'd be interested in the data ie. temp of water vs temp of air for various flow rates.

Thought's ??

Mountain Rescue

Very interested in your post,I renovated a 1960s buglow at the end of 2013. Dry lined, pumped cavity, installed tripled glazed passive windows,done as mush airtightness as possible and installed a mhrv,I feel the hrv is dropping the temp in the house by to much and was only this weekend trying to come up wit a cost effective way of adding some heat to the ducting for the cooler months,I had the exact same idea as yourself,install some kind of rad in a insulated box an fit to air intake,I was wondering if I should plumb it or install an electric duct heater?have you gone any further with your idea?

MicktheMan

What kind of temp drop are we talking about?

Before thinking about the boost of air temp, I would ensure that the ducting (supply and extract) is insulated sufficiently & located within the thermal envelope. If any of the ducting is outside the envelope (e.g. in a cold attic) then this needs to be addressed first.

@Tippgaafan: why on the return air duct?

Dardania

you may have an inefficiency by installing the heater on the return duct - would be more optimal to install on the supply.

Sometimes boilers need a minimum load to run constantly - what does your boiler modulate down to? (should be on the manufacturer's website / technical instructions etc.)

be careful of causing a low humidity discomfort....drying out the air like that

what's the thermal insulation & air tightness like? most people tolerate lower temps at night, as they're under bed covers keeping them warm. Might be better to focus the money in insulation?

Mountain Rescue

Not sure if tippgaafan is still around.would agree with installing some sort of heater on the air intake.for my situation during the winter months when the heat is on for a few hours in the evening say 3 hours and the house is comfortable 20/21degrees by morning the temp can be as low as 13/14 degrees.when i done up the house in 2013,I dry lined with 50mm insulation,pumped the cavity with 100mm, put about 500mm insulation in the attic sealed all wall and ceiling junctions with airtight tape,and sealed around all windows with tape, pumped behind the switchs with a silicone and sealed around light fittings,I haven't got round to air tightness test yet,I feel the house should be a little more comfortable than it is.maybe I'm wrong,maybe I should have gone further down the passive line but money wasn't there unfortunately. So here I am now trying to see if there is anything I can do.just yesterday I was looking at the air intake,it's on the north side of the house which never gets sun and is always cold,was thinking of maybe piping it to the south side which is usually about 9 degrees warmer(any thoughts on that?)

MicktheMan

Mountain Rescue wrote: »

1. for my situation during the winter months when the heat is on for a few hours in the evening say 3 hours and the house is comfortable 20/21degrees by morning the temp can be as low as 13/14 degrees.when i done up the house in 2013,I dry lined with 50mm insulation,pumped the cavity with 100mm, put about 500mm insulation in the attic sealed all wall and ceiling junctions with airtight tape,and sealed around all windows with tape, pumped behind the switchs with a silicone and sealed around light fittings,I haven't got round to air tightness test yet,I feel the house should be a little more comfortable than it is.maybe I'm wrong,maybe I should have gone further down the passive line but money wasn't there unfortunately.
2. So here I am now trying to see if there is anything I can do.
3. just yesterday I was looking at the air intake,it's on the north side of the house which never gets sun and is always cold,was thinking of maybe piping it to the south side which is usually about 9 degrees warmer(any thoughts on that?)

1. When you drylined you significantly reduced the thermal mass (i.e. thermal storage) of the house. So when the heating is on, there is limited storage capacity in the house to store the heat for later release back into the house. This could well be the cause of the large temp drop (even with good air tightness levels) .
2. How is your heating controlled? Perhaps you could investigate using an intelligent chronostat (digital time and thermostat) with a reduce setpoint temp for the night time. This could be more cost effective than trying to create a completely new distribution / control system.
3. Makes no difference.

galwaytt

I know of a house in Clare and apart from a wood pellet stove in the sitting room, a heating coil like you suggest is the sole method of heating in the house, and it works well.


The wood pellet stove and solar panels heat water in a buffer tank, and the heating coil in the HRV system draws heat from the buffer which is fed through the HRV system.