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All systems go

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Some buildings, by their nature, tend to have larger energy requirements. Occupied around the clock, with occupants who feel the cold, nursing homes are a case in point. John Hearne visited a north Dublin building where a range of different sustainable technologies operate in tandem to deliver the residents’ heating and hot water requirements

A new nursing home in Castleknock, County Dublin combines a solar system, air to water heat pumps, a micro-CHP unit and condensing gas boilers to deliver one of the most cost-effective heating and hot water solutions for a facility of this kind you’re ever likely to see. Energy savings in the order of 40 per cent are expected from a system whose ingenuity lies not in any one technology but in a minutely engineered synthesis of four separate systems.

Elm Green Nursing Home is a three storey, 100-bed facility which includes 15 staff apartments and 27 independent living units linked by a glazed corridor to the main structure. The building itself, though it incorporates a reasonably beefed-up insulation spec, is of largely conventional construction. A steel frame on the ground floor supports a concrete deck on the first floor – this to facilitate underfloor heating – while all other structures are timber frame. A U-value in the walls of 0.25W/m2K is achieved through a combination of rigid polyurethane and fibreglass, while a figure of 0.16W/m2K in the roofs comes courtesy of 350mm of cross-laid rock wool. There’s also low energy lighting throughout. Billy Malone of BEM Electrical, who designed the lighting specification, explains that all internal lights are 2D high frequency fittings, varying in intensity between 16W and 38W. Motion sensors control operation in circulation areas. Externally, 100W fittings are controlled through photocells and timeclocks.

The real story however is in the plant-room, and a heating system that was designed and built by mechanical services engineer, Paul Lynch. “You’ve a solar heating system, you’ve a micro-CHP, you’ve gas boilers and you’ve six heat-pumps, and they’re all integrated together,” he explains. “Basically, we have certain criteria we have to meet. We have to heat the nursing home with underfloor heating, we’ve to heat the 27 apartments and we have to heat the staff quarters, so we have a substantial heat requirement.” The bulk of that heat is carried to occupants via 4,700m2 of underfloor heating in the ground and first floor slabs of the main building, supplied by long-established heating technology company Henco Ireland, a Blackrock-based company who also offer renewable energy systems. The secondary heat load to the apartments and staff quarters is carried by radiators. Each of these solutions was primarily chosen to reflect the particular kind of use to which each space is put, Lynch explains. “I put radiators into the staff quarters, for a start because it’s timber frame construction, and it would have been a bit difficult at the time to put in underfloor heating, but it’s mainly from a response point of view, in the sense that, the staff are not going to be up there all day. What you really want is when they come in that they can flick the switch, or set the timer. There’s a time-clock for each apartment, all the rads are thermostatically controlled and there’s also a valve in the plant room that’s weather compensated.”

The usage profile of the nursing home itself also dictated the combination of underfloor and heat-pumps. “We’re driving the underfloor heating all the time through the heat pumps, but we’re only bringing it up to about 30 degrees to maximise the COP (estimated at between 3.5 and 4 at that temperature). And it’s efficient because the building is a 365 day building,” Lynch says. “You never have a peak demand; there’s a constant call for heat. This solution is ideal for the likes of prisons, hospitals and nursing homes. Normally, when we’re designing a system, say an office or a warehouse, you have to have huge boiler capacity so that on a Monday morning, you can bring the place up to temperature quickly, but here, you don’t need the same kilowatt capacity because demand is flat.” The heating load is demand led. Thermostats in each of the zones in the nursing home call for heat as required, and within the plant room, the system responds incrementally, calling on more heating and circulation power as it’s needed. The six 28kW Dimplex heat-pumps, which were supplied by Geothermal Solar in Kildare, operate in cascade, minimising current drawdown. A series of inverter or variable speed pumps in the plant-room each control four underfloor heating manifolds. As zones heat up and require less heat to maintain temperature, each manifold shuts down, sending a signal back to the inverter pump that less power is now necessary. In this way, power scales up and down in smaller increments, giving greater control over heat distribution and power output. “Your normal scenario in a heating situation,” says Lynch, “is your pump is driving all the time. If you have 100 radiators, what happens is, as the rads shut down, the pump is still cranking as hard as ever, so you end up actually getting noise in your pipes. Here, as the building comes up to temperature, the pumps go to sleep, they crank back down to the minimum flow rate, and as demand flow rate increases, they drive up.”