The Heat Pump Conundrum
Older, existing properties have much less insulation and are less well sealed than a new build property, and so, consume more energy thus produce more CO2. These properties would benefit the most from energy saving measures.
However, older existing houses present challenges to the introduction of heat pumps. Their heat losses are higher, producing a higher heat demand of the system. Compared to a boiler, heat pumps produce ‘low grade’ heat – typically 40~50°C compared to a boilers 70°C- and so are less well suited to heating an older property.
How to Square the circle?
Emitters – a matter of degree
With a lower grade of heat available, there are limiting factors in the choice of emitters.
read more below …
Underfloor heating (UFH) is seen as the natural partner of heat pumps.
UFH has to be limited in its operating temperature, to avoid damaging the floors and so is well suited to working with a heat pumps naturally lower operating temperatures.
An underfloor heating (UFH) system generally operates at between 40°C & 45°C creating a surface temperature of between 27°C (for wooden floor coverings) and 35°C (for tiled surfaces). This equates to between 55 watts per square metre and 80watts per square M of heated floor (figures of 100w/M are often quoted but this is usually before the surface covering is applied).
In older, draughty properties this is often not enough. Whilst UFH is relatively straight forward to install in a new build with concrete screed, or a new extension with a tiled floor, it becomes significantly more problematic for a retrofit project, or if wood, laminate or carpet are the preferred final covering.
Oversized Radiators
If upheaval is to be avoided, one solution is oversized radiators; basically, just a bigger version of the existing radiator to compensate for the reduction in flow temperature.
Whilst from a plumbing point of view this is the easiest solution it is not without its drawbacks.
Space
With space often at a premium, giving over even more wall and use-able floor space to a radiator probably wouldn’t win many plaudits from the homeowner; most are trying to either hide the radiator with decorative covers or preferably lose it all together.
Fitting one which may be up to twice as large just to accommodate the use of a heat pump may meet with some resistance.
Secondly, despite being universally known as a radiator, most radiators are in fact convectors, in that they rely more on air movement (or convection currents) to distribute the heat around the room. Radiators rely on a higher differential in surface temperature to the air around them to create the lift or thermal currents that moves the warm air around.
With a surface temperature of 40°~45°C, the difference is not that great (approximately half that of a normal boiler and radiator system) and so the convection currents created are much weaker.
This can result in a phenomenon known as micro-climating whereby the warm air mainly circulates in close proximity to the radiator itself due to the lack of lift, resulting in poor distribution of heat.
In some cases, this has led to developers fitting two and sometime three low temperature radiators around the main living spaces to combat the poor heat distribution.
Fan Assisted Radiators
In order to reduce the installed size of the radiator, some manufacturers have produced smart or fan assisted radiators. They compensate for the lower water temperature produced by the heat pump. Fan assisted radiators use a fan to blow air, drawn into the house across a heating element, and then out through the grilles on the top.
This has the advantage of improving the heat distribution by projecting the warm air and reducing the overall size of the unit compared to a conventional oversized radiator.
In contrast, there is the need for an electric supply (to power the controls and the fan) meaning a straight swap from a conventional radiator is not always possible, and the fans may cause disturbance if located in a bedroom.
Aesthetically, fan assisted radiators may not be to everyone’s taste and will still occupy wall space and limit furniture positions in the same way that a conventional radiator does.
Skirting heating of the past
After Victorian cast iron radiators but before mass manufactured pressed steel radiators and central heating became common place, skirting heating was indeed a relatively popular way to heat a home.
However, it fell out of favour in the 60’s and 70’s as the cost of steel pressed radiator fell dramatically as central heating became mainstream.
Skirting heating survived mainly for use in offices and commercial premises, marketed under the names CopperRad or FinRad and usually utilising aluminium fins or wafers on a central copper pipe, in order to maximise the heat output per foot. Aesthetically they were challenging and prone to infiltration from dust and debris as the cold air was drawn up from the floor and out of the grilles, or articles were dropped inside.
As insulation levels in properties improved, the heat load required decreased accordingly, and a new opportunity to provide an alternative solution to convector radiators emerged.
Not anymore … more
Skirting heating
Radiant skirting heating is effectively a radiator (in the true sense of the word) that has been squashed and stretched and formed to look like a conventional skirting board profile.
Taking up no wall space, having a low water volume and thus being very responsive compared to UFH, and being a simple above ground installation makes skirting heating a very practical emitter to use with a heat pump.
